That's a kick ass trailer Winbean. Visceral, everybody dies! By the way, growing up I used to sing the song they have as the soundtrack for this as I learned it as a young boy, it was a very popular Russian antiwar children's song.
en.wikipedia.org/wiki/May_There_Always_Be_Sunshine
Kelly's Heroes is on the IMDB list I posted but there are few other comedies there as they seem to be among the rarest of the WWII Genres.
Talking with Relik before I made this post, we determined that "Best WWII Movie" is too wide a designation. Of course people can compose a list but there are so many sub genres to be found that its hard to include all the good ones. Here's a few of those sub genres we looked at.
WWII Movie Subgenres
1 The Battle movie. These are movies that explore a single battle, through single or multiple viewpoints. Examples: Midway (1976 and 2019), Battle of the Bulge (1965), A Bridge too Far (1977) etc...
2 The Mission Movie. A group is put together to accomplish a single mission. Saving Private Ryan (1998), The Dam Busters (1955), Where Eagles Dare (1968), The Guns of Navarone (1961) etc... Maybe here you could include The Heist Movie where a group of soldiers finds out about treasure and seeks it out like Kelly's Heroes (1970).
3 The Escape/Prison Movie. Again self explanatory. Examples include: The Great Escape (1963), Stalag 17 (1953), The Bridge on the River Kwai (1957), Victory (1981) etc...
4 The Holocaust Movie. This is mostly self explanatory. Examples include: Schindler's List (1993), Life is Beautiful (1997), The Pianist (2002), Sophie's Choice (1982) etc...
5 The "Trying to stay out of the war but get dragged in movie" Examples include: Casablanca (1942), Empire of the Sun (1987), The English Patient (1996) etc...
6 The Assassination Movie. These are where people join a mission simply to kill or kidnap important leaders. Examples include: The Dirty Dozen (1967), The Eagle Has Landed (1976), Inglourious Basterds (2009)
7 The Submarine Movie. Again another common theme which is self explanatory. Examples include: Das Boot (1981) and U-571 (2000)
8 So many other sub genres too. Like the Bomber Crew, The Fighter Pilot (s), The Disillusioned with War Soldier or Antiwar Movie like Die Abenteuer des Werner Holt (1965).
Just looking at this makes the idea of a making a comprehensive list seem silly.