Many of the soldiers in the film are armed with M1A1 Thompson submachine guns noted by their triangular "bunny ear" sight housing including Pvt. Kelly (Clint Eastwood) and Master Sgt. "Big" Joe (Telly Savalas). These guns were specially requested by Kelly for his special squad to find the gold behind enemy lines, which is why they are not armed mainly with M1 Garand rifles like a normal squad. Throughout the film, the M1A1 Thompsons sometimes switch with older M1 Thompson submachine guns with more complex bolts and cheaper bolted peep sights on the back with no protective housings.
The older M1 Thompson submachine guns are seen in the hands of many soldiers, which had more complex bolts and cheaper style peep sights which have no protective housings like the M1A1s. They are mainly seen switching with the M1A1s throughout the film as a continuity error.
Pvt. Fisher (Dick Balduzzi) uses an M1 Carbine which he usually keeps fitted with an M8 rifle grenade launcher fixed on the barrel as his main weapon throughout the film.
Despite the fact that the M1 Garand rifle was the most commonly employed weapon in the U.S. Army during WWII, the rifle is seldom seen and is never used or fired in the film. Many are seen slung on the backs of extras as they march past Kelly in his jeep when he talks with Big Joe. It is seen in the hands of Pvt. Babra Gene Collins at the beginning of the film.
The Belgian FN BAR Type D light machine gun takes the place of the American Browning BAR for the film with noticeable differences such as a larger wooden forend, a removable barrel, cooling barrel fins, a pistol grip, and a dust cover which were added to the gun by the Belgian army for it to meet their military requirements. It is most notably seen in the hands of Pvt. Petuko (Perry Lopez), Pvt. Mitchell (Fred Pearlman) and Pvt. Grace (Michael Clark).
The aircraft version of the Browning M2 is seen mounted on top of the Sherman tanks under Sgt. Oddball's (Donald Sutherland) command, noted by their perforated barrel shrouds. During the assault on the town, Pvt. Kelly (Clint Eastwood) mans the M3 mounted on Oddball's tank and fires it at a Tiger Tank before the Sherman destroys it with a shot to the weak rear end. The guns appear to be fitted with a muzzle blank adapter which dimensions are clearly smaller than a .50 caliber to allow enough pressure to cycle the gun, though the blanks being fired are indeed .50 BMG blanks.
The Browning M1919A4 machine gun is seen as one of the weapons carried by Kelly's squad and when their vehicles are destroyed by friendly plane fire, SSgt. Crapgame (Don Rickles) is ordered by MSgt. Big Joe to lug the .30 cal around, which he hates and throughout the film he tries to pawn the gun off on others to carry. Like the M3, the 1919 guns in the film are fitted with muzzle blank adapters, more notable on the .30 cals because the muzzles would normally recoil on the real gun but the adapters clearly block them from sight.
Mk 2 Hand Grenades are standard issue with the U.S. Army and all the members of Kelly's squad use them, most notabley MSgt. Big Joe a few times in the film.
One interesting consequence of filming in Yugoslavia was the usage of eastern European weapons in the place of American ones. The production used the Polish WZ. 35 VIS Pistol (also referred to widely and incorrectly as the "Radom") to impersonate the American M1911A1 handgun (which would be standard issue to American forces). American Soldiers such as Pvt. Kelly (Clint Eastwood) and Platoon Sgt. Bellamy (Len Lesser) are seen with Polish WZ. 35 VIS pistols as their sidearms.
Pvt. Gutowski (Richard Davalos), the squad sniper, is armed with a Mosin Nagant M91/30 sniper rifle outfitted with a 3.5PU scope. It would be far more accurate if he had been using a Springfield 1903A4 sniper rifle. This was never explained by the filmmakers. There's a remote possibility though that Gutowski captured the rifle from a German sniper, who originally captured the rifle from a Red Army sniper on the Eastern Front. According to Capt. Clifford Shore, the author of With British Snipers to the Reich, many German snipers were using captured Soviet-made Mosin-Nagant sniper rifles alongside the Mauser Kar98k sniper rifle in Western Europe during the later years of World War II. However there are many reasons why American command would frown upon 'scrounging' for such a weapon (lack of ammo in that caliber would be one reason) and also the American Army in Southern France was very well supplied, and except for grabbing a foreign weapon in the heat of battle, U.S. Forces would not be allowed to scrounge foreign weapons except perhaps as souvenirs.
The Karabiner 98k was the standard rifle of the German army during WWII but like many old WWII movies, the MP40 is shown as the main weapon of the Germans (see also Where Eagles Dare), which was the exact opposite in real life. In this film, the Kar98k is actually seldom seen. In real life, the MP40 was issued the same way the Thompson M1A1 was issued in the American Army. Submachine guns were for NCOs, Officers, Members of Crew served weapons, or specified members of special units like Airborne troops. Every enlisted man was not issued a submachine gun. Of course, towards the end of the war, the Wehrmacht issued anything they had left in inventory to every able bodied soldier.
Inaccurately shown as the most prolific weapon of the German Army, the MP40 submachine gun is seen in the hands of almost all the German soldiers in the film. Noteworthy is that all of the German Soldiers armed with the MP40 submachine gun aren't wearing the MP40 magazine pouches, but the Black leather tri-pouch for the Karabiner 98K.
Four barreled AA/AT (anti-aircraft/anti-tank) Flakvierling 38s are seen used by the Germans when Oddball and his tanks assault the train station and they are all destroyed before they inflict any damage on the tanks.
Oddball (Donald Sutherland) keeps a Luger P08 pistol as his sidearm of choice, which somehow seems to fit his quirky character. Instead of keeping it in a Luger holster, he keeps it in the poorly fit U.S. M1916 holster.
In one scene, a U.S. soldier can be briefly seen in the background with a Lee-Enfield No.4 rifle slung over his shoulder - which is odd to see because the Lee-Enfield No.4 rifle was the standard-issue rifle of the British Army and British Commonwealth forces serving in Western Europe during World War II. There were literally hundreds of Yugoslavian 'extras' as American soldiers and this anachronistic rifle was more than likely handed out as 'filler' for the many M1 Garand or the Springfield 1903 rifles. It is just unfortunate for the filmmakers that the one bit of footage clearly showing the British rifle is seen in the film.
