The Germans historically used air-cooled Maxim LMG 08/15 machine guns on their Fokker biplanes and triplanes. The guns featured in the movie are either one of two mockup kits. The first is the blank firing version which is achieved by using two submachineguns inside a "shell" made to look like the Maxim. The second is the flame shooting variant, (using gas), that is more faithful to the design of the original Maxim but only fires a gas flame. The revealing mistakes for the blank firing version are easily spotted: The cocking handle on each MG doesn't move when the gun is fired unlike the original. The brass also ejects through the right side of the gun and actually from the middle of the cooling jacket as opposed to the original. Another giveaway is that the barrel of each MG is seen protruding from just above the exact center of the cooling jacket. (In reality, the barrel was at the bottom of the jacket.) Another strong hint that the movie MG's are a mockup is the presence of stick magazines inserted very near where the movie-version MG's is seen ejecting brass. The mockups might are the main reason (at least in part) why the pilots are using a handle to fire the MG's even though the historical aircraft used buttons attached to the flight stick in order to fire the onboard weapons.
The British fighter craft and recon plane is armed with the Lewis aircraft gun which is revealed to be a mockup on all the planes. Besides the general (incorrect) form of the weapon, the main revealer that it is a mockup is that the ammo drum does not rotate while firing.
Error creating thumbnail: File missingAircraft mounted Lewis Gun .303Error creating thumbnail: File missingThe British observer/gunner after being hit by machine-gun fire from Stachel. Note the hose between his hands which leads to the weapon and supplies the gas for the muzzle flame. The front round sight is also incorrect.Error creating thumbnail: File missingA top-mounted "Lewis" on a British S.E.5. The details reveal it is not a genuine Lewis. First of all the wooden stock. Second, note the hose which supplies the muzzle flame.
Error creating thumbnail: File missingVickers Mk1 Machine Gun - .303 BritishError creating thumbnail: File missingNote the soldier manning the MG on the right. His helmet is tilted to his left in an awkward angle. Seconds later this screencap was taken an explosion takes place just to the left of the soldier meaning the tilted helmet was most likely done for safety reasons.
Vickers Machine Gun (mockup)
The British are also seen using the Vickers MG, though they all seem to be mockups made to shoot flame only.
Error creating thumbnail: File missingVickers gun with ribbed water jacket - .303 BritishError creating thumbnail: File missingA British pilot of the S.E.5 aircraft has a Vickers MG mounted bottom right. For some reason, the weapon is never seen fired in the finished movie. The gas hoses for both the top mounted Lewis gun and the Vickers MG are clearly seen though.Error creating thumbnail: File missingAn Anti-Aircraft crew man their dual Vickers MG during an attack by Stachels Squadron. Note the gas hoses hanging down in the center.
Unknown Light Machine Gun
The Lewis Gun is replaced in some scenes by what appears to be a genuine (but unknown) LMG. It is modified to fire flames only from the muzzle and the hose is visible in most scenes.
Lee-Enfield No.4 Mk.I is carried by German troops. The rifle is also seen in the hands of Bruno Stachel (George Peppard) during his own time in the trenches. The movie was shot in the Republic of Ireland and there was a lack of genuine German firearms (with one exception) for the shoot so older Irish Defence Forces weapons were substituted for German weapons. The bayonet is a "No 9 MK1" which was issued in 1947.
In a reasonable move made by the producers all the British soldiers are carrying the older Lee-Enfield No.1 Mk.III* with it's original sword bayonet to distinguish it from the German soldiers who (due to lack of German authentic weapons) carry the Lee-Enfield No.4 Mk.I with it's shorter bayonet.
Error creating thumbnail: File missingBritish soldiers await the German attack with their Mk.III*'s. Note the very long bayonet which would prove too long and cumbersome in trench warfare. It's successor is ironically carried by the Germans with their Mk.IV short bayonet.
Lee-Enfield Mk.I (probable)
During the hand to hand combat scenes at least one German is seen with what appears to be an older Lee-Enfield Mk.I. The rifle is identifiable via the magazine cut-off switch visible and the portruding barrel which none of the later Lee-Enfield models had. The bolt action handle, (for the combat scenes), seems to have been removed though the bolt itself seems to be in place.