Factual error: Throughout the first battle at "Hacksaw Ridge" some of the men are seen pulling the pins of grenades with their teeth. In actuality, the pins on the grenades (both modern and old ones) take at least 7 pounds of force to release the pin. If someone did that, they'd either cause severe damage to their teeth or maybe lose a couple.
Factual error: Once the men first climb up to "Hacksaw Ridge," the camera pans over numerous corpses. One of them has an M1 Helmet lying on its top to where the liner is seen. The liner has the web suspension straps cross each other instead of being tied in the center. This means the liner is a Vietnam era type, and not World War II.