Submarine Design and Construction Fundamentals

Submarine Design and Construction Fundamentals

Richard Skiba

Copyright © 2024 by Richard Skiba

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Skiba, Richard (author)

Submarine Design and Construction Fundamentals

ISBN 978-1-7637173-3-6 (Paperback) 978-1-7637173-4-3 (eBook) 978-1-7637173-5-0 (Hardcover)

Non-fiction

Contents

Preface

1.Introduction to Submarine Engineering

2.Basic Principles of Submarine Architecture

3.Hydrodynamics and Submarine Performance

4.Propulsion Systems for Submarines

5.Submarine Power and Electrical Systems

6.Life Support Systems

7.Weapons and Combat Systems

8.Navigation and Communication Systems

9.Submarine Safety and Damage Control

10.Materials and Manufacturing in Submarine Construction

11.Designing for Stealth and Acoustic Signatures

12.Autonomous and Unmanned Submarine Systems

13.Environmental and Operational Constraints

14.Project Management in Submarine Construction

References

Preface

Submarine construction is a complex process that requires specialized shipyards, highly skilled labour, advanced technology, and stringent quality controls. Due to the complexity of building submarines, only a limited number of countries have the industrial, financial, and technical capacity to produce them. These nations build submarines for their own navies and, in some cases, for export to other countries. The global demand for submarine construction has grown in recent years, driven by strategic needs, national security concerns, and maritime defence policies.

Due to the specialized nature of submarine construction, only a limited number of countries possess the necessary industrial, financial, and technical capabilities to produce these vessels. This exclusivity is often a reflection of national security priorities and strategic military needs. For instance, Indonesia's strategic plan emphasizes the necessity of developing indigenous submarine capabilities to enhance its maritime defence posture [1]. Similarly, the global landscape of submarine construction is shaped by geopolitical dynamics, where nations not only build submarines for their own naval forces but also engage in export activities to bolster their defence partnerships [1, 2]. The demand for submarines has surged in recent years, driven by heightened national security concerns and evolving maritime defence policies including the importance of sea power in contemporary defence strategies [3].

The growing complexity of maritime security challenges has led to an increased emphasis on submarine capabilities as a deterrent and a means of asserting national interests in contested waters. The strategic implications of submarine construction are further explored in the context of international relations, where nations seek to enhance their maritime capabilities in response to perceived threats [3]. This trend underscores the critical role that submarines play in modern naval warfare and the broader context of national defence strategies.

Submarine construction is a critical aspect of naval defence capabilities for many countries around the world. The United States, United Kingdom, France, Russia, China, Germany, South Korea, India, and Australia are among the key players in this field, each with specific facilities and strategic focuses.

In the United States, submarine construction is predominantly carried out at two major shipyards: General Dynamics Electric Boat in Connecticut and Newport News Shipbuilding in Virginia. These facilities are responsible for the production of advanced nuclear-powered submarines, including the Virginia-class and Columbia-class submarines, which are integral to the U.S. Navy's strategic capabilities. The collaboration between these shipyards and the Navy ensures that the U.S. maintains one of the most sophisticated submarine fleets globally, focusing on both attack and ballistic missile submarines.

The United Kingdom's submarine construction is centred at BAE Systems’ shipyard in Barrow-in-Furness, where the focus is primarily on nuclear-powered submarines. The UK is currently developing the Astute-class SSNs and the Dreadnought-class SSBNs, which are set to replace the aging Vanguard-class submarines. These submarines are essential components of the UK's strategic deterrent force, underscoring the importance of maintaining a robust submarine fleet.

France's submarine construction capabilities are based at Naval Group’s shipyards in Cherbourg. The French Navy produces both nuclear-powered and conventionally powered submarines, with notable projects including the Suffren-class (Barracuda) SSNs and the Scorpène-class diesel-electric submarines, which are also exported to various countries, including India and Brazil. This dual focus on domestic and export markets illustrates France's strategic approach to submarine technology and defence.

In Russia, submarine construction occurs at the Sevmash shipyard in Severodvinsk and Admiralty Shipyards in Saint Petersburg. The Russian submarine program features a diverse array of nuclear-powered and diesel-electric submarines, such as the Yasen-class SSNs and Borei-class SSBNs. Russia continues to advance its submarine technologies while also exporting submarines like the Kilo-class to nations including India and Vietnam, reflecting its ongoing commitment to maintaining a formidable naval presence.

China's submarine construction is primarily conducted at state-owned shipyards, notably the Bohai Shipyard and Wuchang Shipyard. The Chinese Navy focuses on both nuclear and conventional submarines, including the Type 093 SSN and Type 039A/B diesel-electric submarines. China's expanding submarine fleet is a crucial element of its maritime strategy, aimed at establishing dominance in the Indo-Pacific region.

Germany specializes in the production of advanced diesel-electric submarines, particularly the Type 212 and Type 214 classes, built by ThyssenKrupp Marine Systems (TKMS). These submarines are recognized for their air-independent propulsion (AIP) systems, which enhance their operational capabilities by allowing them to remain submerged for extended periods. Germany's submarine exports to countries like Norway and Israel further highlight its technological advancements in this field.

In South Korea, submarine construction is carried out at Daewoo Shipbuilding & Marine Engineering (DSME) and Hyundai Heavy Industries (HHI). The country has developed advanced diesel-electric submarines, such as the KSS-III class, for both domestic use and export, including contracts with Indonesia. This development reflects South Korea's growing presence in the global submarine market.

India's submarine construction efforts are spearheaded by state-run shipyards, particularly Mazagon Dock Shipbuilders (MDL) in Mumbai. India is focused on developing both conventional and nuclear-powered submarines, including the domestically-built Arihant-class SSBNs and the licensed production of Scorpène-class submarines in collaboration with France's Naval Group. This strategic focus aims to enhance India's naval capabilities and self-reliance in defence manufacturing.

Australia is currently modernizing its submarine fleet under the AUKUS agreement, which will enable it to acquire nuclear-powered submarines. Although Australia lacks the capability to build nuclear submarines domestically at present, it is investing in submarine infrastructure and workforce development to facilitate co-production with the United States and the United Kingdom.

The global demand for submarine construction is significantly influenced by various factors, including strategic deterrence, conventional defence needs, geopolitical tensions, and technological advancements. This demand reflects the evolving nature of maritime security and the strategic imperatives of nations worldwide.

Strategic Deterrence and Nuclear Capability: The role of submarines, particularly ballistic missile submarines (SSBNs), is paramount in the nuclear deterrence strategies of countries with nuclear arsenals, such as the United States, Russia, China, France, and the United Kingdom. These submarines provide a credible second-strike capability, which is essential for maintaining strategic stability. The construction and modernization of SSBNs are critical to ensuring that these nations can effectively deter adversaries through assured retaliation [4]. The integration of advanced technologies into these submarines enhances their operational effectiveness, thereby sustaining the demand for their construction [5].

Conventional Defence and Maritime Patrol: For countries that do not possess nuclear capabilities, the focus shifts towards acquiring conventional submarines, such as diesel-electric and air-independent propulsion (AIP) submarines. These vessels are increasingly sought after for their effectiveness in coastal defence, surveillance, and maritime patrol operations. Their quieter operation and smaller size make them particularly suited for littoral engagements, which are becoming more relevant in contemporary naval warfare [6]. Nations like Japan and South Korea are actively expanding their submarine fleets to enhance their maritime security and operational readiness [7].

Geopolitical Tensions and Regional Rivalries: The rise of geopolitical tensions, especially in the Indo-Pacific region, has led to an escalation in submarine procurement and modernization efforts among regional powers. Countries such as India, Australia, and South Korea are investing heavily in their submarine capabilities to counter perceived threats from China and to assert their maritime sovereignty [8]. This regional arms race is characterized by a strategic emphasis on enhancing naval capabilities, which directly correlates with increased demand for submarine construction [9].

Export Market for Submarines: The global submarine market is also shaped by the export activities of countries with advanced submarine manufacturing capabilities, such as France, Germany, and South Korea. These nations actively engage in selling submarines to countries looking to bolster their naval forces, including Brazil, Egypt, and Indonesia [10]. The export of submarines not only supports the economies of these manufacturing countries but also contributes to the proliferation of advanced naval technologies globally [11].

Technological Advancements and Modernization: The demand for next-generation submarines is being fuelled by technological advancements, particularly in areas such as air-independent propulsion (AIP) and unmanned underwater vehicles (UUVs). These innovations are critical for enhancing the stealth and operational capabilities of submarines, making them more effective in modern warfare scenarios [6]. Countries are increasingly focused on modernizing their fleets to incorporate these advanced systems, which further drives the demand for submarine construction [5].

Increased Focus on Stealth and Underwater Warfare: The operational effectiveness of submarines is heavily reliant on their stealth capabilities. As nations recognize the importance of covert operations in naval warfare, there is a growing investment in stealth technologies, including advanced sonar systems and acoustic coatings. This emphasis on stealth not only enhances the survivability of submarines but also increases their strategic value, thereby contributing to the rising demand for their construction [6].

The purpose of this book on submarine design is to cater to a broad spectrum of readers, each with specific needs and interests related to submarine engineering, operations, and strategic applications. By exploring the fundamental and advanced principles of submarine design, this book seeks to equip a variety of professionals and enthusiasts with the knowledge required to engage with this highly specialized field.

Foremost, naval architects and marine engineers will find this book invaluable. It provides in-depth insights into the principles of modern submarine design, addressing structural considerations, propulsion systems, and the integration of advanced technologies. For those tasked with designing, constructing, and maintaining submarines, this book will serve as an essential resource to stay abreast of innovations that drive the future of submarine capabilities.

Military personnel and defence analysts will also benefit greatly from this book. It sheds light on how submarine design impacts tactical operations, including stealth, endurance, and weapon deployment. For naval officers, strategists, and defence experts, this book provides information on the interplay between submarine capabilities and naval warfare, strategic deterrence, and power projection.

This book is equally vital for submarine technicians and maintenance crews. By offering detailed explanations of how submarines operate and how various systems function, the book enables technicians to better troubleshoot, repair, and upgrade submarines. Understanding the intricacies of submarine architecture can lead to more efficient maintenance and higher operational readiness.

For students and academics in naval engineering or defence studies, this book serves as both a foundational text and a deep dive into advanced concepts in submarine design. It supports academic development by offering a comprehensive overview of engineering practices, historical innovations, and the future of submarine technologies, making it an excellent reference for research or coursework.

Additionally, defence industry professionals and contractors will find this book particularly useful. It highlights the technical requirements, challenges, and innovations involved in submarine construction, helping these professionals contribute to and manage projects more effectively. Understanding the complexities of submarine design enables better decision-making and successful project execution.

Beyond professionals, this book caters to submarine enthusiasts and historians who are interested in the evolution of submarine technology and its role in military history. The book provides a thorough examination of how design innovations have influenced naval outcomes, offering a deeper appreciation of the strategic and technological milestones in submarine development.

For policy makers and government officials involved in defence procurement, maritime strategy, or military policies, the book offers a clear understanding of submarine design complexities. This knowledge supports more informed decision-making when approving defence budgets, choosing submarine technologies, or negotiating international treaties.

With the growing relevance of autonomous underwater vehicles (AUVs) and unmanned systems, researchers in this field will also benefit from the book’s exploration of how traditional submarine design principles apply to unmanned technologies. The insights provided can inform the development of next-generation underwater drones and robotics.

Environmental scientists and marine conservationists will find value in understanding how submarine design interacts with marine ecosystems. This book offers a perspective on the environmental impact of submarine operations, helping advocate for more sustainable practices that minimize underwater disruption.

Finally, investors and stakeholders involved in naval defence projects will gain from this book’s technical insights into submarine design. Equipped with this knowledge, they can better evaluate the potential risks, innovations, and successes of projects they are funding or supporting.

This book serves as a comprehensive resource for a wide-ranging audience, including engineers, military professionals, students, industry leaders, policymakers, and enthusiasts, all seeking a deeper understanding of the complexities and innovations shaping submarine technology today.

Chapter 1

Introduction to Submarine Engineering

Submarines are underwater self-propelled crafts that are designed and built to perform underwater operations for a stipulated amount of time [12].

A submarine is a specialized watercraft designed to operate underwater. Unlike surface ships, submarines can submerge and travel beneath the ocean for extended periods. They are typically used for military purposes, such as reconnaissance, stealth attacks, and deterrence, but also serve in scientific research, underwater exploration, and deep-sea salvage operations.

Figure 1: Remora 2000 research submarine of the Hellenic Centre for Marine Research. Montereypine, CC BY-SA 4.0, via Wikimedia Commons.

Submarines are equipped with advanced navigation, communication, and propulsion systems that allow them to manoeuvre underwater. They maintain buoyancy through ballast tanks, which can be filled with water to submerge or filled with air to surface. Many submarines are nuclear-powered, allowing them to stay submerged for months at a time without needing to refuel. Others are diesel-electric, which requires surfacing more frequently to recharge batteries.

Figure 2: The SS-083 ROKS Dosan Ahn Chang-ho Cruising above Water. ROK Ministry of National Defense's public work is used according to Korea Open Government License (KOGL) (KOGL Type 1, via Wikimedia Commons.

Their hulls are built to withstand the extreme pressure of deep-sea environments, and they are often armed with torpedoes or missiles, making them a strategic asset in naval warfare. The submarine design consists of a single or double-hull system that houses all the necessary systems and manpower required for completion of their mission.

When designing a submarine, the first and foremost objective is to ensure that the submarine meets the functional requirements of the customer. This includes considering what the submarine will be used for, such as military defence, scientific exploration, or commercial purposes like deep-sea mining or salvage operations. The functional design must support the specific operational needs, whether it's stealth, speed, endurance, or specialized equipment for research. Therefore, the design process involves a deep understanding of the intended mission of the submarine and aligning the design features—such as size, shape, propulsion, and onboard systems—to achieve that purpose effectively [12].

The next critical objective is ensuring that the submarine's design can be constructed with the resources that are available. This involves considering the capabilities of the shipbuilding facilities, the availability of materials, and the technical expertise required for the construction. Even if the design is perfect in theory, it must be feasible in practice, which means using materials and technologies that are accessible and familiar to the manufacturing team. This often includes balancing cutting-edge innovations with tried-and-tested techniques to ensure the submarine can be built efficiently and without unnecessary delays [12].

Lastly, the cost of the submarine project must be acceptable to the customer. Submarine construction is an expensive and complex undertaking, so the budget plays a crucial role in design decisions. Designers must carefully consider the cost of materials, labour, testing, and any technological systems that will be incorporated into the submarine. The goal is to deliver a design that not only meets the customer's operational needs but also stays within a reasonable budget. Balancing functionality, feasibility, and cost ensures that the final submarine design satisfies the customer both in terms of performance and affordability [12].

Submarine design is critically important because it directly impacts the vessel's functionality, safety, and effectiveness in fulfilling its mission. Several key reasons highlight the importance of submarine design:

Operational Effectiveness: The design of a submarine determines how well it can perform its intended mission, whether it's military operations like surveillance, reconnaissance, and deterrence, or civilian applications such as deep-sea research and exploration. A well-designed submarine ensures that it meets specific functional requirements, such as stealth, speed, endurance, and the ability to deploy weapons or scientific instruments. For military submarines, effective design allows them to operate undetected, project power, and serve as strategic deterrents, while for civilian submarines, it enables safe and effective exploration of underwater environments.

Survivability and Safety: Submarines operate in one of the most hostile environments on Earth: deep underwater, where high pressures, limited oxygen, and the risk of mechanical failure can be deadly. Proper design ensures that the submarine can withstand the extreme conditions of deep-sea operations, including pressure resistance, structural integrity, and reliable life support systems. Submarine design must also account for crew safety during extended missions, with provisions for emergency systems, escape routes, and redundant systems to prevent catastrophic failures.

Stealth and Detection Avoidance: For military submarines, stealth is one of the most critical aspects of design. Submarines must be able to operate undetected, avoiding sonar detection, radar, and other surveillance systems. This involves designing the hull shape to minimize noise and hydrodynamic drag, using soundproofing materials, and incorporating advanced propulsion systems to reduce acoustic signatures. Effective submarine design gives navies a strategic advantage by enabling covert operations and reducing vulnerability to enemy attacks.

Technological Integration: Submarine design must integrate a wide range of advanced technologies, including navigation systems, sonar, communication equipment, weapons systems, and propulsion technologies. These systems must be seamlessly integrated into the submarine’s design to ensure they function efficiently and reliably under demanding conditions. Effective design ensures that the submarine can accommodate new technologies, allowing for upgrades over time without significant alterations to the vessel’s structure.

Resource Efficiency and Cost Management: Designing submarines involves balancing the need for cutting-edge technology with the constraints of available resources and budget. Proper design allows for efficient use of materials, energy, and manpower while keeping construction and operational costs within acceptable limits. This includes considerations for ease of construction, maintenance, and the long-term lifecycle of the submarine. Effective design helps prevent cost overruns and ensures that the vessel delivers value over its operational lifespan.

Environmental Impact: Submarine design also plays a role in minimizing the environmental impact of underwater operations. This includes the use of clean, efficient propulsion systems (such as nuclear reactors or advanced battery technologies) that reduce emissions and environmental disturbances. Additionally, civilian submarine designs may focus on non-invasive exploration techniques to preserve fragile underwater ecosystems.

Strategic and Political Implications: Submarine design influences a nation’s naval power and strategic capabilities. Submarines are often a key component of national defence, especially in maintaining a nuclear deterrent. The design of a country’s submarine fleet can impact international relations, military alliances, and strategic posturing. A well-designed submarine force strengthens a nation’s ability to project power, protect its interests, and maintain security in contested regions.

Submarine Types

Submarines can be broadly categorized into military and civilian types, each designed with distinct purposes, capabilities, and features to meet their respective objectives. They can be classified into several types based on their design, propulsion systems, and operational roles. The primary categories include military submarines, research submarines, and tourist submarines, each with distinct functionalities and technological requirements.

Military Submarines

These are further divided into nuclear-powered and diesel-electric submarines. Nuclear submarines, such as the Russian Alpha class, utilize liquid metal coolants like Lead-Bismuth Eutectic (LBE) for their reactors, allowing for extended underwater endurance and speed [13]. They are designed for stealth and can carry out a range of missions, including anti-submarine warfare, reconnaissance, and strategic deterrence through nuclear capabilities. Diesel-electric submarines, while generally slower and with limited underwater endurance compared to their nuclear counterparts, are often quieter and less expensive to operate, making them suitable for coastal defence and operations in shallow waters [14].

Military submarines are engineered primarily for defence and offensive operations, serving as strategic assets in naval warfare. The main types include:

Attack Submarines (SSNs and SSKs): These are designed for hunting and destroying enemy submarines and surface ships. They can be powered by nuclear reactors (SSNs) or diesel-electric engines (SSKs). Nuclear-powered attack submarines can operate for extended periods underwater due to their virtually unlimited range and endurance, while diesel-electric submarines, though quieter, require more frequent surfacing to recharge batteries. Attack submarines are often equipped with torpedoes, cruise missiles, and sometimes special operations forces for covert missions.

Ballistic Missile Submarines (SSBNs): These submarines are built to carry and launch nuclear ballistic missiles. They are the core of a nation’s nuclear deterrence strategy, capable of remaining hidden underwater for long durations to ensure a second-strike capability in the event of a nuclear attack. SSBNs are usually large, heavily armed, and designed to maintain stealth while on patrol in deep ocean waters.

Cruise Missile Submarines (SSGNs): These submarines are designed to launch a large number of conventional or nuclear-tipped cruise missiles, typically targeting land-based facilities. SSGNs can also support special operations forces and intelligence-gathering missions. Like SSBNs, they are often nuclear-powered to provide extended endurance and operational range.

Midget Submarines: Smaller in size, midget submarines are used for special operations, including reconnaissance, insertion of special forces, or laying mines. They have limited operational range and are often carried by larger submarines or surface ships to their mission areas.

Unmanned Underwater Vehicles (UUVs): These are autonomous or remotely operated submarines used for reconnaissance, mine detection, or other missions without risking crewed vessels. UUVs are becoming more prevalent in modern navies due to advancements in underwater drone technology.

The acronyms for various types of submarines stand for the following:

SSN: Ship Submersible Nuclear - A nuclear-powered attack submarine.

SSK: Ship Submersible Killer - A diesel-electric attack submarine (also referred to as a hunter-killer submarine).

SSBN: Ship Submersible Ballistic Nuclear - A nuclear-powered submarine that carries and launches ballistic missiles.

SSGN: Ship Submersible Guided Missile Nuclear - A nuclear-powered submarine designed to carry and launch cruise missiles.

Each acronym reflects the type of propulsion system (nuclear or diesel-electric) and the primary function of the submarine (attack, ballistic missile, or cruise missile).

The classification of submarines into categories such as Attack Submarines (SSNs and SSKs), Ballistic Missile Submarines (SSBNs), Cruise Missile Submarines (SSGNs), Midget Submarines, and Unmanned Underwater Vehicles (UUVs) is widely acknowledged by many navies and defence organizations around the world. However, these classifications are not entirely universal. Different nations may adopt variations in how they categorize their submarine fleets or use alternative terminology, depending on the specific roles or capabilities that their submarines are designed to fulfill. This classification system is crucial for understanding the strategic roles and capabilities of different submarine types. For instance, Attack Submarines (SSNs and SSKs) are primarily designed for anti-submarine warfare and land attack missions, while Ballistic Missile Submarines (SSBNs) serve as a strategic deterrent by carrying nuclear missiles [15]. Similarly, Cruise Missile Submarines (SSGNs) are equipped to launch precision strikes against land targets, showcasing the versatility of modern submarine warfare [15].

Attack Submarines (SSNs and SSKs) are classified based on their power source and intended mission. Nuclear-powered attack submarines (SSNs) are common in the fleets of major powers like the United States, Russia, the United Kingdom, and France. These submarines offer extended operational endurance due to their nuclear propulsion. In contrast, diesel-electric attack submarines (SSKs) are more prevalent in smaller or regional navies, as they are quieter and less expensive to operate. Despite this general classification, some countries may have unique designations for their attack submarines, particularly when differences in size, range, or operational focus come into play.

Figure 3: Mooring lines secure the nuclear-powered attack submarine USS ALBANY (SSN 753) to the pier for the vessel's commissioning ceremony. The U.S. National Archives, Public Domain, via Picryl.

Ballistic Missile Submarines (SSBNs), sometimes referred to as boomers, form a key component of the nuclear triad in major powers like the United States, Russia, China, France, and the United Kingdom. This classification is widely accepted across the globe because SSBNs play a crucial role in maintaining nuclear deterrence. Their strategic purpose—carrying and launching nuclear ballistic missiles—is well-defined, making the SSBN classification nearly universal among countries that operate them.

Figure 4: USS Kentucky (SSBN 737) returns to homeport at Naval Base Kitsap-Bangor, Wash. U.S. Navy, CC BY 2.0, via Flickr.

Cruise Missile Submarines (SSGNs) are also a significant category, primarily utilized by countries with advanced naval capabilities such as the United States and Russia. These submarines are either converted from SSBNs or specifically designed to launch conventional or nuclear-tipped cruise missiles. Although the SSGN classification is widely recognized, not all countries operate submarines exclusively designated as SSGNs. Instead, some nations may rely on multi-role submarines that fulfill various tasks, including launching cruise missiles, without assigning a specific SSGN classification.

Midget Submarines are smaller in size and are employed by several nations for special operations, coastal defence, and intelligence-gathering missions. Countries such as North Korea, Iran, and some European states make use of these submarines for specific tactical purposes. The classification and terminology of midget submarines may vary by country, with some navies referring to them as mini-submarines or using other localized terms based on their operational role, size, or technology.

Unmanned Underwater Vehicles (UUVs) represent an evolving class of submarines in modern naval operations. These autonomous or remotely operated underwater vehicles are increasingly used for reconnaissance, mine detection, and surveillance missions without putting human crews at risk. While the UUV classification is becoming more established, terms like Autonomous Underwater Vehicles (AUVs) or Remotely Operated Vehicles (ROVs) are sometimes used interchangeably, depending on the level of autonomy and the specific mission profile.

While these submarine classifications—SSNs, SSKs, SSBNs, SSGNs, Midget Submarines, and UUVs—are widely recognized and utilized by the world's leading naval forces, there can be slight variations in terminology and classification depending on a nation's naval doctrine, fleet capabilities, and operational focus. Nevertheless, these general categories remain consistent across major submarine-operating nations, reflecting the distinct roles that different types of submarines play in naval operations.

Civilian Submarines

Civilian submarines are designed for peaceful purposes, including research, exploration, and commercial activities. They are typically smaller and less heavily armed but feature advanced technology for their specific uses. The main types include:

Research Submarines: These submarines are used by scientific institutions to explore and study underwater environments, including deep-sea ecosystems, geology, and underwater archaeology. They are equipped with scientific instruments, cameras, and robotic arms to collect data, samples, and footage. Examples include Alvin and DSV Limiting Factor, which are designed for deep ocean exploration. These submarines are equipped with advanced scientific instruments and are used for oceanographic research, underwater exploration, and environmental monitoring. They can operate at various depths and are designed to withstand extreme underwater conditions. The wakes produced by these vehicles in stratified fluids are of particular interest, as they influence hydrodynamic performance and can affect the accuracy of data collected during missions [16]. Research submarines often collaborate with underwater sensor networks to gather data on marine ecosystems and geological formations [17].

Tourism Submarines: Designed for short, shallow dives, these submarines provide a unique experience for tourists, allowing them to explore coral reefs, shipwrecks, or marine life in areas where diving would be challenging. These submarines are pressurized to ensure passenger safety and offer panoramic views through large windows. These are designed for civilian use, allowing tourists to explore underwater environments safely. They are typically smaller and equipped with large viewing windows, providing an immersive experience of marine life. Unlike military and research submarines, tourist submarines operate in shallower waters and are not equipped for deep-sea exploration [14].

Commercial Submarines: These submarines are used in industrial applications such as underwater construction, maintenance, and repair, typically in the oil and gas industry. They are used to inspect pipelines, deep-sea drilling operations, and subsea infrastructure. Some are also used for underwater salvage operations, recovering sunken ships or treasure from the ocean floor.

Personal Submarines: Personal or recreational submarines are small, privately owned submarines used by individuals for underwater exploration. These submarines typically have limited range and depth capabilities but offer private owners the ability to explore underwater locations for leisure or personal projects.

Hybrid and Emerging Types

With advancing technology, new types of submarines are emerging that blur the lines between military and civilian uses. These include multipurpose submarines designed for dual-use operations, capable of performing both scientific research and military reconnaissance. Additionally, innovations in autonomous underwater vehicles are pushing the boundaries of what submarines can achieve in both civilian and military sectors, leading to increasingly sophisticated and capable submarines across the spectrum of uses.

The development of submarines has been significantly influenced by advancements in materials science and communication technologies. For instance, the use of fibre-reinforced composites has improved the structural integrity and performance of submarine components [18]. Moreover, underwater communication remains a challenge due to the absorption of electromagnetic waves in seawater, leading to the exploration of acoustic and optical communication methods to enhance operational capabilities [19, 20].

History of Submarine Development

Submarines first became a significant force in naval warfare during World War I (1914–18), primarily due to Germany's effective use of them to target and destroy surface merchant vessels. Their main weapon was the torpedo, a self-propelled underwater missile that allowed submarines to strike ships without being detected. This strategic use of submarines continued into World War II (1939–45), where they played an even larger role in both the Atlantic, where Germany's U-boats targeted Allied shipping, and the Pacific, where American submarines attacked Japanese vessels. The 1960s marked a major advancement in submarine design with the advent of nuclear-powered submarines. These vessels could stay submerged for extended periods, sometimes months, and were capable of launching long-range nuclear missiles without surfacing, solidifying their place as a cornerstone of strategic military power. Armed with torpedoes as well as anti-ship and anti-submarine missiles, the nuclear attack submarine has since become a critical component of naval warfare [21].

The concept of a submarine, a craft designed to navigate underwater, first emerged in 1578 when British mathematician William Bourne proposed a fully enclosed boat that could submerge and be rowed underwater. His design featured a wooden frame covered in waterproof leather and was intended to submerge by contracting the sides to reduce volume using hand vises. Although Bourne never constructed his design, the idea was later brought to life by Dutch inventor Cornelis Drebbel, who built the first functioning submarine between 1620 and 1624. Drebbel's craft, made of a greased leather-covered wooden frame, was propelled by oars and could reach depths of 12 to 15 feet during trials in the Thames River. King James I of England is said to have even taken a short ride in the craft. Drebbel’s work laid the foundation for future submarine designs, and his success was followed by two larger versions of his original craft [21].

The early 18th century saw a proliferation of submarine concepts, with numerous designs and patents emerging. By 1727, 14 types of submarine boats had been patented in England alone. In 1747, an inventor proposed an innovative submersion method using goatskin bags that filled with water to sink the craft and were then emptied using a twisting rod to bring it back to the surface. This design was an early precursor to the modern submarine ballast tank. By the mid-18th century, over a dozen patents for submarine designs had been granted in England. Nathaniel Symons is credited with building the first working ballast tank system in 1747, using leather bags filled with water to submerge the submarine and a mechanism to force the water out, bringing it back to the surface. Although these early designs showed promise, further advancements stagnated for more than a century until technological progress in propulsion and stability reignited interest [21].

The submarine was first used as an offensive weapon during the American Revolution (1775–83) with David Bushnell’s one-man craft, the Turtle. Built in the shape of a walnut and powered by propellers cranked by hand, the Turtle was designed to approach enemy ships underwater, attach a gunpowder charge, and retreat before the explosion. Although the Turtle’s attack on a British warship was unsuccessful, it marked the first use of a submarine in naval warfare [21].

Figure 5: Full-size model of the Turtle submarine on display at the Royal Navy submarine museum. Geni, CC BY-SA 4.0, via Wikimedia Commons.

Years later, American inventor Robert Fulton experimented with submarine design. In 1800, while in France, Fulton built the Nautilus, a copper submarine with iron ribs, a collapsible mast and sail for surface propulsion, and a hand-turned propeller for underwater movement. The Nautilus could submerge using ballast tanks and maintain depth with a horizontal rudder, the precursor to modern diving planes. Despite successfully sinking a schooner during trials, Fulton’s attempts to use the Nautilus in warfare were thwarted when both France and Britain lost interest in the project. Although he continued his efforts in the United States, Fulton died before his steam-powered submarine could be completed [21].

During the War of 1812, a copy of the Turtle was built and used in an attack on the British ship HMS Ramillies off the coast of Connecticut. The operator managed to bore a hole in the copper sheathing of the warship but failed to attach the explosive due to the screw breaking loose. Despite these early setbacks, the pioneering efforts of inventors like Bushnell and Fulton laid the groundwork for future submarine development, proving the potential of underwater vessels in naval warfare [21].

During the American Civil War (1861–65), the Confederacy sought unconventional methods to counter the Union Navy's superior strength, particularly the blockade of Southern ports. One such attempt involved the use of submarines. In 1862, Horace L. Hunley from Mobile, Alabama, financed the construction of a Confederate submarine named Pioneer. This 34-foot craft was powered by a hand-cranked propeller operated by three men. Although some records suggest the Pioneer was lost during a dive, it was likely scuttled to avoid capture when Union forces took control of New Orleans [21].

Figure 6: The Confederate submarine Pioneer's measured drawings given to William Shock, Fleet Engineer of the Western Gulf Blockading Squadron in 1862. William Shock, Public domain, via Wikimedia Commons.

Following the Pioneer, the same builders developed a second, more advanced submarine. This 25-foot iron boat was designed to be powered by a battery and electric motors, but suitable motors could not be found. Instead, a hand-cranked propeller operated by four men was again used. Unfortunately, this submarine sank in heavy seas off Mobile Bay while attempting to engage the enemy, though no lives were lost in the incident [21].

The third Confederate submarine was the H.L. Hunley, a modified iron boiler that was lengthened to about 36 to 40 feet. It featured ballast tanks and a system of weights to submerge the vessel. Powered by eight men cranking the propeller, the Hunley could reach speeds of four miles per hour. Its weapon was a torpedo containing 90 pounds of gunpowder, which was towed behind the submarine on a 200-foot line. The plan was for the submarine to dive beneath an enemy warship and drag the torpedo into its hull. After a successful test against a barge, the Hunley was transported to Charleston, South Carolina. Despite suffering several accidents, including three sinkings that resulted in numerous crew deaths, including Hunley himself, the Hunley continued its operations.

On February 17, 1864, the Hunley attacked the Union warship Housatonic in Charleston Harbor. It used a torpedo mounted on the end of a long spar to strike the warship. The explosion ignited the Housatonic's magazines, sinking the ship in shallow water and killing five men. However, the Hunley was also destroyed in the explosion, resulting in the loss of its entire crew [21].

Around the same time, Wilhelm Bauer, a Bavarian artillery non-commissioned officer, was making his own advances in submarine design. Bauer built two submarines: Le Plongeur-Marin (1851) and Le Diable-Marin (1855). The first boat sank in Kiel Harbor on February 1, 1851, but Bauer and his two assistants managed to escape from a depth of 60 feet after being trapped for five hours. His second submarine, constructed for the Russian government, proved more successful, reportedly completing 134 dives before being lost at sea. In September 1856, during the coronation of Tsar Alexander II, Bauer even submerged his submarine in Kronshtadt harbor with musicians on board, who played the Russian national anthem underwater—an impressive feat that could be clearly heard by those aboard nearby ships.

A major limitation of early submarines was the challenge of propulsion. In 1880, English clergyman George W. Garrett successfully operated a submarine powered by steam from a coal-fired boiler, featuring a retractable smokestack. However, the fire had to be extinguished before the craft could submerge, as leaving it lit would consume all the available air inside the submarine. Even so, the remaining steam allowed the vessel to travel several miles underwater. Around the same time, Swedish gun designer Torsten Nordenfelt constructed a steam-powered submarine driven by twin propellers. His design included vertical propellers that enabled the submarine to submerge to depths of 50 feet. Nordenfelt’s craft was also among the first to feature a practical torpedo tube, and several nations adopted his design.

Efforts to improve submarine propulsion continued. In 1864, two French naval officers built the Le Plongeur, a 146-foot submarine powered by an 80-horsepower compressed-air engine. However, the air tanks were quickly depleted whenever the craft got underway. The development of the electric motor offered a breakthrough in propulsion. The Nautilus, built in 1886 by two Englishmen, was an all-electric submarine powered by two 50-horsepower electric motors and operated using a 100-cell storage battery. This submarine could achieve a surface speed of six knots (approximately 6.9 miles per hour or 11.1 kilometres per hour), but its range was limited to 80 miles before requiring a battery recharge. In France, Gustave Zédé launched the Gymnote in 1888, which was also propelled by an electric motor. Though it was highly manoeuvrable, the Gymnote had issues with control when diving.

Figure 7: Photo of the French submarine Gymnote in Page's Magazine No. 2 from 1902. That issue had an article about the development of submarines. Note that this photo shows the small conning tower that was added in 1898. archive.org, Public domain, via Wikimedia Commons.

The late 19th century was a period of rapid development in submarine technology, particularly in France. Zédé collaborated on various designs sponsored by the French navy, leading to the successful launch of the Narval in 1899. Designed by naval engineer Maxime Laubeuf, the Narval was a double-hulled submarine, 111.5 feet long, that used a steam engine for surface propulsion and electric motors when submerged. The ballast tanks were located between the double hulls, a feature still in use today. The Narval completed numerous successful dives and marked a significant step forward in submarine design. French advancements continued with the Sirène-class steam-driven submarines completed between 1900 and 1901, and the Aigrette, launched in 1905 as the first diesel-powered submarine in any navy [21].

In the United States, rival inventors John P. Holland and Simon Lake also made significant contributions to submarine design. Holland, an Irish immigrant, launched his first submarine in 1875. His designs were notable for combining water ballast with horizontal rudders for diving. In 1895, the U.S. Navy commissioned Holland to build a submarine, the Plunger, which was to be powered by steam on the surface and electricity when submerged. However, the project encountered numerous challenges and was eventually abandoned. Holland later built another submarine, the Holland, at his own expense. Launched in 1897 and accepted by the U.S. Navy in 1900, this 53.25-foot submarine was powered by an electric motor underwater and a gasoline engine on the surface. The Holland was armed with a bow torpedo tube and two dynamite guns, and it proved to be a successful vessel, undergoing several modifications to test different configurations of propellers, diving planes, rudders, and other equipment [21].

Holland’s chief competitor, Simon Lake, constructed his first submarine, the Argonaut I, in 1894. Powered by a gasoline engine and electric motor, the Argonaut I was designed primarily for undersea research. In 1898, it became the first submarine to operate extensively in open sea conditions, traveling under its own power from Norfolk, Virginia, to New York City. This achievement preceded the voyages of the French Narval and demonstrated the potential for submarines in long-range missions. Lake’s second submarine, the Protector, was launched in 1901.

Figure 8: The submarine Narval (S 64) docked at the port of Melilla; it is the fourth and final unit of the Delfín Class. Bruno Cleries, upload by Basilio, CC BY-SA 3.0, via Wikimedia Commons.

At the turn of the century, most major naval powers were investing in submarine development, with Britain being a notable exception until 1901 when the Royal Navy ordered five submarines based on Holland’s designs. Germany, too, entered the submarine race, completing its first submarine, the U-1, in 1905. The U-1 was 139 feet long and powered by a heavy oil engine on the surface and an electric motor when submerged. It was armed with one torpedo tube. These early submarines set the stage for the 20th-century submarine, which would be propelled by diesel engines on the surface and electric motors underwater, submerging by taking on water ballast and using diving planes, and armed with torpedoes to sink enemy ships. Despite these advancements, life aboard early submarines was far from comfortable; the quarters were cramped, often wet, and smelled of diesel oil [21].

Figure 9: German submarine U 1 on trials. navyphotos.co.uk, Public domain, via Wikimedia Commons.

By the outbreak of World War I, all major naval powers had incorporated submarines into their fleets. However, these early submarines were relatively small and primarily intended for coastal operations, with their military value still viewed with some scepticism. One notable exception to this coastal focus was the German Deutschland class of merchant U-boats. These submarines were significantly larger, measuring 315 feet in length and featuring two spacious cargo compartments. Capable of carrying 700 tons of cargo, they could travel at speeds of 12 to 13 knots on the surface and seven knots while submerged. Eventually, the Deutschland itself was converted into the U-155 by fitting it with torpedo tubes and deck guns, and along with seven similar submarines, it played a combat role during the later stages of the war. In contrast, the standard submarine of World War I was smaller, typically just over 200 feet long and displacing less than 1,000 tons on the surface [21].

Before the war, submarines had been primarily armed with self-propelled torpedoes designed to attack enemy vessels. However, as the war progressed, submarines were also equipped with deck guns, which allowed them to surface and signal enemy merchant ships to halt for inspection (a policy used earlier in the war) or to sink smaller or unarmed ships without expending torpedoes. Most war-built submarines had one or two deck guns of three- or four-inch calibre, though some later German submarines, including the Deutschland class in its military configuration, carried larger 150-millimeter guns.

An important variation in submarine armament during the war was the development of mine-laying submarines. The Germans constructed several specialized submarines equipped with vertical mine tubes that allowed them to covertly lay mines in enemy harbors. Some U-boats could carry as many as 48 mines in addition to their torpedoes, greatly enhancing their strategic impact.

Another significant innovation during World War I was the introduction of submarines designed to combat enemy submarines. British submarines sank 17 German U-boats during the conflict, leading to the development of the R-class submarine, specifically designed for anti-submarine warfare. These submarines were relatively small, measuring 163 feet in length and displacing 410 tons on the surface, and featured a single propeller (while most submarines of the time had two). The R-class submarines could reach speeds of nine knots on the surface using diesel engines, but once submerged, their large batteries powered electric motors that allowed them to achieve an impressive underwater speed of 15 knots for up to two hours. This made them both highly manoeuvrable and fast, particularly in comparison to other submarines of the era, which typically achieved submerged speeds of around 10 knots until after World War II. The R-class submarines were also equipped with advanced underwater listening equipment, known as asdic or sonar, and were armed with six forward torpedo tubes, making them formidable weapons. Although they arrived too late to have a significant impact on the war, they pioneered a new concept in submarine development [21].

With the exception of the British Swordfish and K-class submarines, all World War I-era submarines used diesel engines for surface propulsion and electric motors for submerged operations. The Swordfish and K-class submarines were intended to operate as scouts for surface warships and required higher speeds, which were achievable only with steam turbines at the time. These submarines could reach surface speeds of 23.5 knots, while their electric motors allowed for submerged speeds of up to 10 knots [21].

Figure 10: German Cargo Submarine Deutschland 1916-22. tormentor4555, Public Domain, via Flickr.

During the period between World War I and World War II, interest in submarines remained strong among the world’s navies. Countries such as Britain, France, and Japan continued to build improved submarine models, while the U.S. Navy introduced its first large, long-range submarine, the Argonaut, in 1928. At 381 feet long and with a displacement of 2,710 tons on the surface, the Argonaut was armed with two six-inch guns, four forward torpedo tubes, and could carry 60 mines. This submarine became the largest non-nuclear submarine ever built by the U.S. Navy and paved the way for the highly successful Gato- and Balao-class submarines used during World War II.

In the 1930s, the Soviet Union also focused on building submarines, primarily small coastal craft, as part of an effort to strengthen its naval power without investing heavily in surface warships. However, despite producing a large number of submarines, the Soviet vessels were unsuitable for operations against the German Navy. The crews were often poorly trained, and their bases were frequently blocked by ice, limiting their effectiveness [21].

World War II saw widespread submarine campaigns across all the world’s oceans. In the Atlantic, the primary German U-boat was the Type VII, a relatively small yet highly effective craft when employed properly. The Type VIIC variant was 220.25 feet long, with a surface displacement of 769 tons. Powered by diesel-electric machinery, it could reach speeds of 17 knots on the surface and 7.5 knots submerged. Its armament included a 90-millimeter deck gun, various anti-aircraft guns, and five torpedo tubes. These submarines, manned by crews of 44, had a surface endurance of 6,500 miles at 12 knots but could remain submerged for less than a day when traveling at four knots [21].

The German Type XXI represented the ultimate development of diesel-electric submarines during the war. Measuring 250 feet long and with a displacement of 1,600 tons, this submarine could achieve submerged speeds of 17.5 knots for over an hour, travel underwater at six knots for two days, or creep at slower speeds for four days. Fitted with snorkel devices, the Type XXI did not need to fully surface to recharge its batteries. Its operating depth was an impressive 850 feet, more than double the norm at the time, and it was armed with four 33-millimeter guns and six forward torpedo tubes, carrying 23 torpedoes. Had the war continued past the spring of 1945, Allied forces would have faced significant challenges in combating these advanced submarines [21].

Another notable German innovation during the war was the Walter turbine propulsion plant. Developed by scientist Hellmuth Walter, this system allowed submarines to use steam turbines while submerged by employing oxygen generated from hydrogen peroxide. The V-80, an experimental submarine built in 1940, could reach submerged speeds of over 26 knots for short periods. Later, Walter-propelled Type XVII combat submarines achieved 25 knots underwater, with trials showing speeds of 20 knots for five and a half hours. However, these advanced submarines, like the Type XXI, were not ready for widespread use by the time the war ended.

One of the most significant German innovations of the war was the schnorchel (or snorkel) device, originally conceived by Dutch officer Lieutenant Jan J. Wichers in 1933. The schnorchel allowed submarines to operate their diesel engines while submerged, drawing in fresh air through a tube. The Dutch Navy began using this technology in 1936, and after falling into German hands in 1940, it was widely adopted by German U-boats. The schnorchel enabled U-boats to recharge their batteries at periscope depth while minimizing the risk of detection by Allied radar.

In the Pacific, the Japanese Navy deployed a diverse range of submarines, including aircraft-carrying submarines, midget submarines, and human torpedoes launched from larger submarines. One notable Japanese class was the I-201, a high-speed submarine that was 259 feet long with a displacement of 1,291 tons. This submarine could reach 15 knots on the surface using diesel engines and 19 knots submerged for nearly an hour, thanks to its large batteries and electric motors. The I-201 was armed with two 25-millimeter guns and four forward torpedo tubes, carrying ten torpedoes.

Figure 11: Japanese Submarine HA-201(SENTAKA-SHO-class) near Sasebo. Unknown author, Public Domain, via Wikimedia Commons.

The U.S. submarine campaign in the Pacific during World War II was highly successful, primarily utilizing the Gato- and Balao-class submarines. These submarines were around 311.5 feet long, displaced 1,525 tons, and were powered by diesel-electric machinery, allowing for surface speeds of 20 knots and underwater speeds of nine knots. The main difference between the two classes was their operating depth, with the Gato class reaching depths of 300 feet and the Balao class capable of descending to 400 feet. Manned by crews of 65 to 70, these submarines were armed with one or two five-inch deck guns, smaller anti-aircraft weapons, and ten torpedo tubes (six forward and four aft), carrying a total of 24 torpedoes.

After World War II, the Allies quickly adopted advanced German submarine technology. The British experimented with two peroxide turbine-propelled submarines, but the concept fell out of favor due to the unstable nature of hydrogen peroxide and the success of nuclear propulsion in the United States. Meanwhile, the Soviet Union began producing modifications of the German Type XXI submarine, leading to the creation of the Whiskey and Zulu class submarines. Between 1950 and 1958, the Soviets completed 265 of these submarines—more than all other navies combined produced between 1945 and 1970. In total, Soviet shipyards produced 560 new submarines during this period [21].

The U.S. Navy also studied German technology, converting 52 war-built submarines into the Guppy configuration (standing for greater underwater propulsive power). These submarines had their deck guns removed, received streamlined conning towers, and were equipped with larger batteries and snorkels. In some cases, one of the diesel engines and some torpedoes were removed, resulting in increased underwater speeds of 15 knots and improved endurance [21].

While the major powers eventually transitioned to nuclear-powered submarines after the war, many of the world's navies continued to use diesel-electric submarines derived from the fast U-boats of World War II. Several of these submarines were designed and built in West Germany. Though these postwar submarines still use snorkels, advances in radar have made it possible to detect even the small head of a snorkel, just as primitive radars detected surfaced U-boats during the war.

The most significant postwar advancements have been in weaponry and sensors. Deck guns have largely been replaced by antiship missiles, while torpedoes have become much faster, capable of exceeding 50 knots. These torpedoes are guided by self-contained sonar or by electronic commands sent through a wire paid out behind the torpedo. Many submarines are now equipped with cruise missiles or antiship missiles, capable of targeting both land and sea. Submarine sonar technology has also seen significant improvements, enhancing the ability to detect both surface ships and other submarines. Additionally, on the most advanced submarines, traditional periscopes are being replaced by photonic or optronic masts, which project sensors to the surface and relay information electronically to the control room. This eliminates the need for any hardware to pierce the submarine's hull, and these masts are operated using a simple joystick with data displayed on screens throughout the submarine.

While the maximum submerged speed of modern submarines has increased slightly to over 20 knots, endurance at top speed remains similar to what it was at the end of World War II. Improvements in lead-acid battery design have increased endurance at lower speeds, allowing modern submarines to remain submerged at around three knots for up to a week to 10 days. This capability is significant, as it allows submarines to take advantage of changing sea conditions or force surface hunters to disperse. The development of air-independent propulsion (AIP), particularly through fuel cells that generate electricity using stored hydrogen and oxygen, has further extended underwater endurance, with some AIP-capable submarines able to operate at low speeds for as long as a month [21].

As a result, diesel-electric submarines remain quiet and effective platforms, operating stealthily and conserving energy for post-attack escapes. Their electric motors are quieter than nuclear units and can even be shut off to allow the submarine to wait silently for enemy submarines to pass. AIP technology offers additional possibilities, such as long-term operations under ice in polar seas, monitoring coastal shipping in antiterrorist missions, or deploying special operations forces to foreign shores. Modern diesel-electric submarines, whether equipped with AIP or not, continue to be affordable and effective tools for navies worldwide, allowing them to defend their coastal waters against all potential threats, even from nuclear powers [21].

In 1954, with the commissioning of the USS Nautilus, nuclear power became a reality for submarines. The introduction of nuclear propulsion allowed submarines to operate without the need for oxygen, meaning a single power plant could be used both on the surface and while submerged. Moreover, nuclear fuel (enriched uranium) provided power for extended periods, enabling submarines to remain submerged at high speeds indefinitely. This revolutionized submarine warfare. Previously, submarines would approach their targets on the surface to conserve battery power and would only submerge just before reaching the target. Underwater, they had to move slowly—often at two to three knots—to avoid depleting their batteries. Following an attack, submarines would use full underwater power (seven to 10 knots) to evade counterattacks, but this would drain the batteries within one or two hours. As a result, diesel-electric submarines were limited in their ability to engage fast warships, such as aircraft carriers and battleships.

Figure 12: USS Nautilus' (SSN-571). Official U.S. Navy Photograph, Public domain, via Wikimedia Commons.

Nuclear-powered submarines, however, were a game-changer. These vessels could operate freely before and after attacks without worrying about battery depletion and could keep up with fast surface ships. This advantage was demonstrated during the Falklands War in 1982 when the British nuclear submarine HMS Conqueror followed the Argentine cruiser General Belgrano for over 48 hours before closing in and sinking it. Such performance was beyond the capability of pre-nuclear submarines. Nuclear propulsion gave submarine commanders unprecedented freedom to manoeuvre underwater, making fast surface ships vulnerable to attack.

Initially, many navies continued building diesel-electric submarines alongside their nuclear counterparts, but the cost of maintaining both types eventually led some nations to transition entirely to nuclear-powered fleets. The U.S. Navy ceased non-nuclear submarine construction in 1959. Similarly, the Royal Navy, which completed its first nuclear submarine HMS Dreadnought in 1963, eventually focused exclusively on nuclear-powered vessels after briefly building the diesel-electric Upholder class in the 1980s and 1990s. France launched its first nuclear submarine, Le Redoutable, in 1971 and stopped building diesel-electric submarines for its own navy in 1976, though it continued producing conventional submarines for export. The Soviet Union followed a similar path, building both nuclear and diesel submarines, though their primary focus shifted to nuclear power after their first nuclear-powered submarines, the November class, entered service in 1958. Russia, the successor state to the Soviet Union, continued to maintain a mixed nuclear-conventional submarine force post-1991. Meanwhile, China began building nuclear submarines in 1968 while still producing large numbers of diesel-electric vessels, a pattern India followed, launching its first nuclear submarine in 1998.

Figure 13: Le Redoutable at the Cherbourg Maritime Museum, France, 28 May 2008. Hugh Llewelyn, CC BY-SA 2.0, via Wikimedia Commons.

Nuclear reactors power submarines by producing heat through nuclear fission. In a reactor, uranium fuel is surrounded by a moderator (usually water) that slows neutrons and helps sustain the reaction. This water, called primary loop water, is pressurized to prevent boiling and carries the heat to a heat exchanger. The heat is then transferred to a secondary water circuit, which produces the steam that powers the turbine. The primary loop remains sealed, preventing contamination of the rest of the plant.

Water in the primary loop is usually pumped, but some reactors use natural circulation based on temperature differences. In these reactors, cooler water from the heat exchanger is fed into the bottom of the reactor, where it heats up as it passes through the fuel elements. Another type of reactor, the liquid-metal-cooled reactor, uses molten metal to carry more heat than water, enabling more compact turbines. However, this introduces challenges, such as the potential for radioactive leaks and the risk of the molten metal solidifying in pipes, leading to catastrophic failures.

Under the direction of Admiral Hyman Rickover, the U.S. Navy developed both pressurized-water and liquid-metal reactor prototypes. The first two nuclear submarines, the Nautilus and Seawolf, tested these systems, but issues with the Seawolf's liquid-metal reactor led to the abandonment of that