Flight scenes were filmed in replica B-17s using technology known as The Volume (used on The Mandalorian (2019)). The B-17s were suspended 50 ft in the air on a gimbal inside a 360-degree stage of seamless LED panel screens and ceiling. Actors could therefore react to flak explosions, crashes and planes flying in real time as the gimbal simultaneously reacted to scenarios.
Three B-17 replicas were built from scratch for filming use. 2 were exact replicas, the other was slightly larger to allow more room for camera crew to film certain angles of the plane.
Austin Butler watched footage of the real-life Cleven who was interviewed about his time as a bomber pilot when he was in his 80s. The footage helped Austin learn Cleven's speaking cadence and sense of humour.
The 100th Bomb Group became known as "The Bloody 100th" due to the heavy volume of losses it incurred in combat missions and minute percentage of survival.
The series was logistically a huge undertaking with over 3000 crew working on the 9 episodes. Steven Spielberg has said this is the biggest project he's worked on.