The other reviewers have already explained a lot in back story so I won't bother add more details to it, cuz as to whether you can be convinced by the whole story is pure personal preference. Like there's carbon coating applied on inner side of the tanks so the girls won't get injured by real tank ammunition. I'm totally fine with it given that other isekai shows have much more logics and backgrounds. It's only a matter of taking it or leaving it.
The title might give you an impression of a cliche drama from a bunch of moe high school girls but don't let it deceive you. From 1 to 10 you can rate "moe level" at around 3~4. The girls are cute indeed thanks to designing artists but the director doesn't offer much fan service in the script. On the contrary the most exciting parts in the show are tank battles. It has one of the maturest CGI performance I've ever seen. It's impressive to the point that you won't feel it appropriate at all when the 3D tanks move and shoot in 2D backgrounds.
From the historical perspective those tanks in this anime are made as authentic as possible to match real WW2 tanks. Though velocity are not quite historical accurate, they can do some cool manuevers. Combined with the presentation of tank battles those inaccurate parts can be easily forgiven.
Dialogues, dressing and even the names of the girls are deliberately designed. With a bit of Googling you can find that almost every girl in the protagonist's team refer to someone real back in history. I really appreciate the staff members to do that. Those research must have taken a long time.
GuP is so intriguing that I've watched it like more than 10 times and every time I can find some details that I previously overlooked, maybe a team leader making gestures to order other students to shoot in tank battles, or how those tanks run in different scenarios because of different size and weight. It's a shame that with so many 3D animation works in it the production cycle is longer than you'd expect from a conventional JP anime. Now the staff team release an OVA every 18 months or so. Other than that I'm totally satisfied with GuP.
