Factual error: Late in the film, Nicolas Cage throws a grenade to kill the Japanese who have captured Roger Willie. The resulting explosion is a prolonged pyrotechnic plume with petroleum flames bursting out of the ground. WWII grenades didn't produce flames of any kind, and they still don't.
Factual error: Throughout the film, Joe Enders is wearing an M1 Helmet. But his helmet looks like a non-WW2 type and possibly Vietnam era. From the side of the helmet, it is a higher cut along the sides. This is a usual indicator to the era of the helmet, as WW2 M1 helmets are lower along the ears for better protection.
Revealing mistake: When Christian Slater and Roger Willie play a mournful Indian tune in a recorder/harmonica duet, neither actor knows how to play his instrument, and it shows.
Answer: The point of using the Navajo code to call in air strikes was to encrypt what the Marines were requesting without the Japanese being able to decipher what was said. This is critical because during the Battle of Saipan, the Japanese made extensive use of caves and reinforced earthworks to support their artillery positions and machine gun nests. The delay between requesting artillery support and the act of carrying it out allowed the Japanese to withdraw their infantry to relative safety before the fire mission could commence. By using PVT Yahzee and PVT Whitehouse, they were able to circumvent this and request attacks without the Japanese knowing what was coming. The only time Yahzee does not use the code is when he uses the Japanese radio to call off the artillery strikes that were falling short and hitting Marines. This situation required immediate attention and it would not have been appropriate to use the code.
Invader_Gir