Because Mars Attacks! is meant to spoof alien invasion flicks from the 1950s and 60s, the United States Army in the film uses equipment and uniforms that were in use during that time period, in keeping with the production aesthetic. Consequently, all soldiers in the film carry the M14 battle rifle in 7.62x51mm NATO, which had long since been replaced by the M16 rifle family at the time of the movie. During the first encounter with the Martians, Billy Glenn Norris (Jack Black) grabs a discarded M14 and tries to shoot the Martians with it, only to learn it is empty (which causes the magazine to fall out for some reason).
It is interesting to note that very few of the M14s in the film seem to fire blanks; it is often possible to see that the muzzle flashes of some rifles were added in post-production, that the actions do not cycle to eject blank casings, and that the actors playing the soldiers are faking the recoil. Also, the rifle that Billy Glenn Norris field-strips and then re-assembles in his trailer clearly has no selector, which means it is most likely a commercial semi-automatic M14 clone (such as a Springfield Armory M1A or a Norinco M14S).
Error creating thumbnail: File missingM14 rifle 7.62x51mm NATOError creating thumbnail: File missingBilly Glenn Norris holds out an M14 rifle after assembling it while blindfolded. Note the lack of a selector, which suggests the rifle might be a Springfield Armory M1A or Norinco M14S.Error creating thumbnail: File missingU.S. soldiers - all wearing old-fashioned olive drab fatigues and helmets - start firing at the Martians with their M14s after the aliens reveal themselves to be hostile.Error creating thumbnail: File missingAnother view of soldiers firing at the Martians in the first encounter. Though we hear the sound of automatic gunfire in this scene, the soldiers' M14s are clearly not firing - there are no shell casings ejected, the actions don't cycle, and the actors are clearly faking the recoil of the weapons into their shoulders.Error creating thumbnail: File missingBilly Glenn attempts to shoot at the Martians with an M14, only to find out that it's not loaded.Error creating thumbnail: File missingHonor Guards at Billy Glenn's funeral fire M14s into the air. This is one of the few scenes in the entire movie where anyone seems to be firing real, blank-converted M14 rifles (as evidenced by the fact that the rifles very visibly eject shell casings and emit smoke from their muzzles when fired).Error creating thumbnail: File missingU.S. soldiers shooting at the Martians at the Capitol. Note that the muzzle flash of the M14 fired by the soldier on the left is clearly fake.
Browning M2HB
Browning M2HB heavy machine guns can be seen mounted on U.S. Army tanks and jeeps (note that the tanks in the film are also old-fashioned M-41s). When the Martians fry Congress, General Decker (Rod Steiger) gets on a tank and fires one at the Martian space ship. As with most of the film's M14s, the M2HB does not seem to be firing blank ammunition; it ejects no shell casings and the muzzle flash was clearly inserted in post-production.
General Decker welds a pair of M1911A1 pistols akimbo whilst shouting at the Martian leader, which do no harm to the Martians as he's shrunk while firing them and then crushed underfoot. An interesting goof is that while he's firing at the Martians, one of his 1911s clearly goes empty, yet gunshots are still heard, and after a split-second cut to the Martians (with no time to reload), he is shown firing both guns again as though nothing happened.
The Secret Service Agents in the movie all carry Beretta 92FS pistols (even though in real life, the SIG-Sauer P228 would have been standard-issue to the USSS at the time of the movie).
President James Dales (Jack Nicholson)'s Secret Service bodyguard Mitch pulls from his shoulder a Micro Uzi and then fires at the attacking Martians near the end of the film.
Sue Ann Norris (O-Lan Jones) and Mr. Norris (Joe Don Baker) load 12 Gauge double barreled shotguns when preparing to fight the invading Martians, though they don't get a chance to use them as a Martian robot smashes their trailer with them inside. The shotgun loaded by Sue Ann has a very distinctive-looking trigger guard, so hopefully, this will allow somebody to ID it. The one used by Mr. Norris has two exposed hammers, so it's definitely an older-style design.
Mr. Norris throws Richie Norris (Lukas Haas) a shotgun and tells him to "lock and load", but Richie drops it to go and get his grandmother, Florence Norris (Sylvia Sidney). The shotgun appears to be a Winchester Model 1912, judging by the shape of the pump when Richie catches it.
Mr. Norris (Joe Don Baker) can also be seen in the trailer loading an unknown revolver which isn't seen clearly, but appears to be a short-barreled Colt Official Police with a 4" barrel (judging by the shape of the hammer and the half-moon shaped front sight.
