Most of the images at the bus taking recruits to boot camp had to be reversed so that the Australian bus (filmed for the movie) looked like an American bus. The close-up of Dorothy handing over her Bible couldn't be reversed, however, without making the letters appear reversed as well; thus, she begins to hand over the Bible with her left hand, which suddenly looks like her right hand. Actor Andrew Garfield (Desmond Doss) was keen enough to use different hands in the shots to make it look as if he always accepted her Bible with his left hand.
When Doss enters the bus for basic training, he sits on the right side of the bus as he says goodbye to Dorothy, but then he sits on the left side of the bus as it drives away.
When Desmond reads his Bible during a break in the assault on the ridge, a close-up of his hand shows an impeccably clean thumb after treating the wounded as they are covered with blood and mud.
After Doss is assaulted at night by his fellow infantrymen, Sergeant Howell observes his bunk's bloody pillow and sheets. 2 seconds later when Doss emerges from the bathroom, the sheets and pillowcase are completely clean. Everybody else in the barracks was standing at attention so there was no chance of some kind of a miraculous quick-change.
During the first battle scene on Hacksaw Ridge, 'Hollywood' Zane's M1 Garand switches from one with a 'regular' rear sight and missing its front sight post to one with a 'locking-bar' sight and an intact front sight.
Harold Doss wears an Army uniform at the kitchen table when in fact he enlisted in the Navy and served aboard the USS Lindsey.
None of the trainees in Basic Training have the proper haircut.
Tom Doss never asked his former commander to write a letter that stopped Desmond T. Doss from being court-martialed. He did, though, contact the chairman of the church's War Service Commission in Washington, Carlyle B. Haynes, who in turn contacted the regimental commander, Colonel Stephen S. Hamilton, who straightened the things out and gave Desmond a three-day pass to go home and see his brother Harold before Harold returned to the Navy to go overseas.
Shortly after the battle begins, one soldier is seen using a BC-611 "Handie Talkie" to communicate with another soldier who is using an SCR-300 backpack "Walkie Talkie." The BC-611 is amplitude modulated (AM) and the SCR-300 is frequency modulated (FM). It is impossible for those two radios to communicate with each other.
When Doss and others head to basic training on the bus, they are all in uniform. Recruits are not issued uniforms until after they arrive at their training units. They should have still been in their civilian clothes.
Sergeant Howell and others throw mortar shells like hand grenades. Such mortar shells are thought to arm themselves by being fired from a tube and would not explode otherwise. This is untrue. Pull the safety pin and bang the base of the mortar bomb on a hard surface to arm the fuse. Beauford T. Anderson was awarded the Medal of Honor doing this during the same engagement.
The Silver Star Medal was not created until 1932, years after Tom Doss left the Army. Prior to that date, the Silver Star Medal's predecessor, the Silver Citation Star, consisted of a silver star, 3/16 inch in diameter worn on the suspension ribbon of the campaign medal, in this case the WWI Victory Medal; however, after the Silver Star was created, any recipient of the Citation Star could have that decoration upgraded to the Silver Star simply by applying.
During the entire movie, not one US soldier was seen running out of ammunition. The M1 Garands used have 8 rounds en-blocs that eject automatically after the last round is fired. This is never depicted as happening. Sgt. Howell fires what appears to be a M3 sub-machine gun (aka Grease Gun), which have a 30-round detachable box magazine. Despite heavy firing, he never has to reload. Given its cyclic rate, the magazine would be empty after 4 seconds of continuous firing.
After Smitty blows up the pillbox and Sgt Howell orders the men to advance, a soldier can be seen picking up the 30 caliber machine gun by the barrel (01:22:00) with his bare hand without getting burned. Since the machine gun has been firing right up to the advance order, the barrel would be extremely hot. This would be impossible to do without an asbestos glove or a tool to grab it by.
When Desmond leaves for boot camp in the bus and kisses Dorothy goodbye through the window, the mole on Dorothy's neck is on the wrong side. This is because the picture has been flipped due to the movie being made in Australia, and in Australia they drive on the left side of the road. The curb and the doors are on the opposite side of the bus. Meaning to make it look like an American bus, the image needed reversing.
In one of the massive fight scenes with the Japanese, a Japanese soldier is burned with the American flame thrower fire and can clearly be seen with a modern fire-retardant glove on his hand.
Recruits drilling in the background at Fort Jackson use a step, cadence, and arm swing of the Austrailian Army, not the US Army. This reflects the filming location and the extras who, presumably were largely not familiar with the proper US Army "quick time" drill, which has a more natural shorter arm swing and cadence.
When the ships are shelling the edge, one of the ships shown has a 18" gun mount which was on one of the Yamato class Japanese battleships.
Tom Doss appears in his World War I Army uniform wearing the 1939-1945 Croix de Guerre. He should be wearing the 1914-1918 Croix de Guerre for distinguished service in WWI.
The real Desmond T. Doss enlisted and went through basic training in 1942, but during his court martial, numerous officers are seen wearing the Combat Infantryman Badge, a decoration not authorized for wear until November 1943.
As U.S. Army soldiers arrive at Okinawa and march up to the front line from the beaches, an Iowa-class battleship can be seen in the ocean in the background. Although the Iowas did participate in the Okinawa Campaign, the battleship in the film is in its 1980s configuration.
In the opening scene, Desmond reads aloud from Isaiah 40:28-31. The translation he quotes is from the New International Version, first published in the 1970s.
When Sgt. Howell inspects the rope knots the soldiers tied, he comments on Private Rinelli's knot saying he "just strangled himself," comparing his knot to a noose. He then asks "Are you a fan of Benito?," possibly referring to the hanging of Benito Mussolini's body after his death. This would be inaccurate, since the training of Doss' unit in Fort Jackson took place in 1942, and Benito Mussolini was not killed and hung until 1945.
When Doss gets lowered down the ridge, the cables that actually hold up the stretcher are clearly visible next to the ropes in multiple shots.
21:30 the shadow of the camera jib is visible and you can see it moving in the subsequent seconds as the camera pans up to Desmond.
Sgt Howell and his men move forward under heavy fire from a Japanese pillbox. Howell orders a bazooka strike on the pillbox, which blows it to smithereens, revealing a second pillbox behind the first, its machine gun killing more of Howell's men. Instead of simply ordering another quick and effective bazooka strike, Howell inexplicably sends two men crawling under heavy fire toward the pillbox with a satchel charge - which makes no tactical sense in that scenario whatsoever.
The Japanese control the ridge, and there are no US troops permanently based on it, yet the US troops attempt to take the ridge each day by climbing up a huge cargo net on a cliff. It is unlikely that the Japanese troops would leave this in place when it could be disconnected and dropped to the bottom of the cliff.
When a unit from the 96th Infantry Division passes Doss' unit on an Okinawa road and were relieving, one of the 96th's soldiers wears a helmet emblazoned with the golden trapezoid of Doss' 77th Infantry Division.
Though the soldiers on Hacksaw Ridge mention artillery a couple of times, there were no artillery pieces shown or present. All of the bombardment came from the battleships offshore. The correct term to use would be a naval bombardment, not artillery.