Lieutenant Helga Katrina Sinclair's weapon of choice is a Mauser C96 Broomhandle which she is seen with throughout the film waving it around until the climax of the film where she finally uses it to great effect until it runs dry.
Luger P08
Commander Lyle Tiberius Rourke's weapon of choice is a pistol weakly resembling the Luger P08.
Remington 1866 Derringer
The Remington 1866 Derringer is very briefly seen in the hands of Wilhelmina Bertha Packard when the group casts over Milo when they reveal to be mercineries.
PPSh-41
Mole is seen with a PPSh-41, fitted with a drum magazine, during the entering of the Kings room, which wasn't available in 1914 and is an anachronism.
Lewis gun
Seen at the climax of the film where the atlantians battle Rourke, Helga and the soldiers. Rourke fires a hand-hald Lewis gun until it is shot out of his hand by an atlantian's ship.
The Double Barreled Shotgun,Cookie's weapon of choice, briefly seen when revealing to be a Mercenary and when entering the Kings room shouting "room service".
Vickers machine gun
The Vickers machine gun is seen mounted on the back of the last surviving truck of the Mercenaries, where two soldiers are mounting it, never seen being fired.
Flare pistol
Helga's Flare pistol which she uses on two occasions, the first she fires it up the Volcano and the second firing it at Rourke and the Balloon with famous last words "Nothing personal".