Continuity mistake: When that one captain is refusing to obey the orders of Nick Nolte he says the time is 13:21 but his watch says it's actually 14:31. Then a couple of seconds later the time is 14:45. Their whole conversation was shown and there was no time in between and it was much shorter than 15 minutes.
Revealing mistake: During the scene in which the small group of GIs, led by the young go-getter officer played by John Cusack, attack the Japanese hilltop bunkers, they seemed to be equipped with magic bullets. The American soldiers are firing wildly in all directions but seem to drop an enemy soldier with every shot. In some shots, the GI's rifles are not pointing even near where the Japanese soldiers are but the latter obligingly fall dead nonetheless.
Other mistake: When the company makes its first advance up the grassy hill through mortar explosions and flying bodies, as the guy next to Captain Staros takes a turn with the binoculars, watch carefully. You'll see he has them pointed down into the grass, not up the hill where the fighting is occurring. Further, the field has zero visibility from gunsmoke, which would prevent him from seeing anything anyway, even if he did have them properly aimed.