For me the best war or greatest war film ever made is Saving Private Ryan (1998). After constant rewatch, I think it is Steven Spielberg's best film, Also when does Tom Hanks not deliver?
My other best or personal greats will be
The Guns of Naravone (1961)
The Bridge on the River Kwai (1957)
Glory (1989)
I also like some modern new ones from the 2000s
Inglorious Bastards (2009)
1917 (2019)