As the 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.
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.
When Sgt. Howell is inspecting 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 on 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.
A couple of times the soldiers on Hacksaw Ridge mention artillery. 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.
When Doss' unit is passed on a road on Okinawa by a unit from the 96th Infantry Division they were relieving, one of the 96th's soldiers wears a helmet emblazoned with the golden trapezoid of Doss' 77th Infantry Division.
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.
During the basic training segment, Sgt. Howell orders the exhibitionist Private Hollywood Zane to complete the obstacle course while still naked, however, he is only seen completing one part of the course. He is inexplicably absent during the remainder of the course and is not even seen in the background or at the end of the course when the rest of the soldiers are shown gathering together.
When Sergeant Howell is inspecting the recruits during the barracks scene, the naked Milt 'Hollywood' Zane is sweating profusely. When Howell sends the men outside, Zane goes to grab his clothes and his skin is completely dry.
At the beginning of the film, when young Desmond hits his brother with a brick in front of their father, the latter is wearing a bandage on his right hand (he cut himself hours ago). When the father carries the brother to the bed, the bandage is gone.
Shortly after the battle begins, one of the soldiers 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.
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.
During the first battle on Hacksaw, Smitty picks up the upper torso of a dead soldier and uses it as a shield against rifle and machine gun fire. Aside from the fact that most of the full metal jacket munitions fired by Japanese rifles and medium machine guns of that era could easily pass right through an average size human torso, Smitty advances to close range of the enemy, firing his Browning Automatic Rifle. Just by counting the BAR's muzzle flashes, he fires at least 23 times without reloading. The BAR's magazine only holds 20 rounds.
When Doss comes down from Hacksaw first time, it is shown that gallons of water is thrown over his head to wash him. Soft water was a valuable resource. It is highly unlikely that that much water was wasted.
Tom Doss' WWI Victory Medal is shown with three clasps: the France service clasp, the Cambrai combat clasp and the Ypres-Lys battle clasp. Service clasps were not worn if the soldier earned a combat clasp, so the France clasp should not be present. US forces at Cambrai consisted of only the 11th, 12th and 14th Engineer Regiments. Tom has an infantry disc on his collar, not an engineer disc. No US unit is known to have been present at both Cambrai and Ypres-Lys. Additionally, Tom states that he fought at Belleau Wood, so he would have been entitled to wear a Defensive Sector clasp, because there was no specific clasp authorized for that battle.
During the Battle of Okinawa, Doss' unit is informed that they are to relieve the 96th Infantry Division, which was tasked with ascending and securing the Maeda Escarpment ("Hacksaw Ridge"). On their arrival at Okinawa one soldier says "Killjoy was here". The actual term used by soldiers was "Kilroy was here." "Kilroy was here" was an American meme that became popular during World War II; it was typically seen in graffiti.
When Colonel Sangston tell Desmond to take the rifle, he refers to himself as Desmond's company commander. A full bird Colonel would never hold the position of company commander. That position is usually assigned to captains or senior 1st Lieutenants. A Colonel is typically a brigade commander.
The tan uniforms worn by the soldiers during their training at Fort Jackson are an odd shade of brown. They should be khaki, a much lighter color. In addition, most of these uniforms are too baggy, especially those worn by the officers.
The film showing in the theater is the 1943 submarine movie [Link=tt0035799], starring Cary Grant and John Garfield. It was released on December 31, 1943, which would put the theater scene sometime in January. The average temperature in January there is in the forties, which would be far too cold to be going out in shirtsleeves and a summer dresses.
Numerous times during basic training scenes and court marshal scenes soldiers are seen rendering a hand salute in-doors. You do not hand salute in-doors you come to attention.
And you never salute uncovered (without a hat) anywhere. This is something Hollywood refuses to get right in almost all military based memories.
Sergeant Howell and others are shown throwing mortar shells like hand grenades. Such shells would not explode, mortar shells arm themselves by being fired from a tube. Throwing them is like throwing rocks.
At least twice in the movie the Foley editors mistakenly use the sound of an M1 Garand rifle ejecting its clip as the sound of a bullet hitting or passing through a helmet (evident at 1:13:09 and especially at 1:19:27). This sound is very distinctive and fairly high in pitch. At 1:13:25 a much more accurate and lower pitched sound is used to represent the sound of a bullet hitting a helmet.
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.
Sgt Howell and his men are moving 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.
During the entire movie, not one US soldier was seen running out of ammo. The M1 Garands used have 8 rounds en-blocs that eject automatically after the last round is fired. Never saw that happen. Sgt. Howell is seen firing 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 sec of continuous firing..
When Doss is determining that a soldier was dead at the top of the ridge, a very brief shot shows the soldier with normal pupil and iris; subsequent shots avoid showing the eyes. In death, pupils dilate due to muscle relaxation. As a medic, Doss would have known this and realized the patient was still alive at that point.
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 it 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.
Recruits drilling in the background at Fort Jackson are using 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 proper US Army "quick time" drill which has a more natural shorter arm swing and cadence.
When Desmond returns to rescue Sgt Howell, a Japanese sniper attempts to shoot Desmond while Howell watches for the sniper's muzzle flash. Desmond dashes for cover and the sniper shoots and misses while Sgt Howell fires twice at the sniper. During this last exchange of gunfire neither Howell nor the sniper are looking through their rifle sights, they are looking well over the top of them.
When Doss slips into the underground tunnel to escape the Japanese soldiers [1:46:45], the body of a dead Japanese is shown with rats sitting on his chest. The movement of the soldier's belt clearly shows that he is still breathing.