When the cake is brought in during the scene with John Basilone, the flag has 15 stripes.
When the mortar squad hears the Japanese in the bunker, the mortar tube switches between having the cover on and not.
The American flag flying at the airstrip is a 50 star flag, even though the Union contained 48 states in 1944.
When Basilone is hitting golf balls, the dimple pattern is modern and not the pattern used in the 1940s.