Two different figures are given for the casualties suffered by the Rangers during the ambush--776 and 767 (+ 7 survivors).
When Stimmler and Ennis discuss the night reconnaissance of the German works, a man appears behind Sgt Stimmler's shoulder in close shot where no-one was standing in long shot.
Maj Gen Lesley is seen on the deck of the transport putting on a parka on top of his greatcoat. Shortly afterwards, he is on the bridge and the parka has disappeared.
The nickname "Black Devils" (or "Devil's Brigade") was acquired after the battle of Anzio. It would not have used been prior to the battle.
All the tanks used on both sides were postwar US models in different paint schemes--possibly M-47's as used in the film Battle of the Bulge made 4 years earlier. On the tanks masquerading as German 'panzers', clearly visible is the original Browning .50 cal heavy machine guns (without ammo boxes) on the turret, instead of replacing them with WW2 German MG34 or MG42 machines guns.
A shortage of German machine guns must have blighted filming as clearly seen in the ambush scene with the German troops in hollow haystacks - rather than using MG 34 or MG 42 machine guns, they use British Army Mk1 Bren Guns & American M1918 Browning Automatic Rifles (although it could be very loosely argued the Bren guns were captured British munitions from earlier in the war, however there would be ammunition compatibility problems as German 7.92x57 ammunition won't work in .303 weapons).
During the sniper ambush near the end, the last German sniper is firing a bolt action rifle, but makes two quick shots in rapid succession, which is impossible with a bolt action. If a single gun fired the shots, it would have had to have been a semi-automatic rifle.
File covering in the shell holes from an earlier battle, the Americans are shown using a dead casualty as cover. Not only do we not see bullets hitting the corpse, but 7.92mm Mauser bullets easily penetrate a human body or even small trees.
The First Special Service Force patch worn by Rabinoff has the word "USA" below "Canada" and not above.
When the guy is trying to sell stockings to the soldiers, numerous women rush towards him, supposedly to look over the stockings, along with numerous children tagging along with the marching band. However, in the following shot, the guy's back is to the camera and he still holds out a handful of stockings to the soldiers, calling for them to buy them, and no hordes of women surround him.
When Robert Mitchum is in the village speaking with the old man, he utters a short sentence in Italian and his voice is an obvious overdub.
Toward the beginning of the film, Cpl. Jack Rabinoff (Peter Falk) is in the back of a Red Cross ambulance with three prostitutes and grabs a shoebox-sized box labeled "Hershey's Milk Chocolate Multi Pack" with a "1968 design" of the Hershey logo. One of the prostitutes reaches into the box and pulls out a "1968 design" box of Brach's Milk Chocolate Stars. In addition to the two anachronisms, Hershey's and Brach's are two separate companies.
During the sequences at the port where the American and British soldiers are loaded onto ships to be transported to the Anzio landing, the color scheme and hull number configurations on the ships are clearly those of the Italian Navy of the 1960s, not USN and RN ships of World War II.
Some of the rifles shown with the U.S. troops were British SMLE's.
Ranger Tab shown being worn (Black and Gold arc) was not designed and approved for wear until November 1950.
When the U.S. general meets his British counterpart, he salutes first before denying the latter's request. Usually, the subordinate officer salutes first.