In all of Vic Damone's scenes as Corporal Pete Lewis, he is seen wearing a very shiny gold bracelet, including in combat scenes. In reality, no person in combat would have ever been allowed to wear a shiny gold bracelet, nor would they have wanted to, out of concern for the bright glint given off which might betray their position. Damone should have been directed to remove the bracelet during filming.
When Gabaldon visits "Mama san" (Mother Une) at the Internment camp, she says her sons are in Italy. This is prior to Gabaldon enlisting in the Marine Corps. Later, on Saipan, Gabaldon says his brothers are in the 442 Regimental Combat Team. The 442 landed at Anzio in May of 1944. The Marines landed on Saipan in June of 1944. Using the timeline established in the movie, there would not have been enough time for Gabaldon to enlist, go through boot camp and fight in the Battle of Saipan.
When David Janssen's character Bill Hazen is killed, and Jeffrey Hunter's Gabaldon, enraged, rushes the Japanese position, shooting his M1 Carbine continuously, and killing all of the Japanese soldiers in sight. However, he fires more than the maximum thirty shots that could have been held by the largest magazine available for the M1, which held 30 rounds, without any evidence that he might have reloaded.