The Comedian (Jeffrey Dean Morgan) uses an M79 grenade launcher to fire smoke rounds at people trying to vandalize the buildings with the phrase "Who watches the Watchmen?" in the rioting crowds. He even hits one rioter dead on with a smoke round during the "American Dream" scene. It is also seen in his closet when Rorschach (Jackie Earle Haley) is checking out his apartment.
Flamethrower
The Comedian (Jeffrey Dean Morgan) uses a Flamethrower to light his cigar with the pilot and then burn a Victor Charlie soldier while in Vietnam. He can also be seen posing with it in Movie Posters. It appears to be a fictional mockup not specifically based on any real flamethrowers, although it resembles an M2 Flamethrower in the graphic novel.
M1911A1
The Comedian (Jeffrey Dean Morgan) uses his issued M1911A1 sidearm in the film to kill a pregnant Vietnamese woman (Nhi Do) when she slashes him with a broken bottle for leaving her and the baby behind behind. During the film's opening credits, a criminal armed with an M1911A1 is shown being foiled by a young Night Owl I (Clint Carleton). We also see a criminal try to draw a nickel plated 1911 fitted with ivory grips when attempting to kill Dr. Manhattan (Billy Crudup), but is blown up horrifically before he can fire off a shot.
D&L Sports Professional Model Longslides
The Comedian's (Jeffrey Dean Morgan) sidearms right up to his murder are custom 1911-series D&L Sports Professional Model Longslides with ornate smiley-face grips to match the Comedian logo. They have "Nixon 1970" written on the grips, indicating they were a gift from Nixon for serving in the Vietnam war. At the beginning of the film, Comedian tries to bring up one of his 1911s (fitted with a sound suppressor) to combat the attacking assailant in his home but fires off one stray shot to no avail and is disarmed. For the most part, these guns are only seen in his holsters or in a presentation case any other time.
Zastava M70AB2
Vietnamese soldiers destroyed by Dr. Manhattan (Billy Crudup) wield folding stock Zastava M70AB2 rifles noted by their folding grenade launcher sights.
AK-47
A Vietnamese soldier whose leg is blown off (seen in better detail in the Director's Cut) is seen with a milled receiver AK-47 before being burned to death by The Comedian (Jeffrey Dean Morgan).
CAR-15
Seen in the hands of NYPD SWAT and US soldiers in Vietnam are CAR-15 carbines with slab-side receivers and full stocks (as opposed to the more traditional collapsing stock). Based on the fact the weapons actually have safe-semi-full selector switches, they could very well be GAU-5/A models, or at least very close copies.
The Comedian (Jeffrey Dean Morgan) is seen holding a scoped Carcano M91/38 while watching John F. Kennedy's car drive by. This implies that he assassinated JFK rather than, or in partnership with, Lee Harvey Oswald.
Remington 870
In the Director's Cut of the film, prison guards fire Remington 870 shotguns at Night Owl II's (Patrick Wilson) owl ship "Archie" as they spring Rorshach (Jackie Earle Haley) from the prison.
Ithaca 37
The Comedian (Jeffrey Dean Morgan) fires on rampaging crowd members with an Ithaca 37 shotgun. He has loaded it with less-lethal rubber bullets, as sourced from the graphic novel.
Franchi PA3/215
A Franchi PA3/215 is seen in The Comedian's (Jeffrey Dean Morgan) hidden closet armory when Rorschach (Jackie Earle Haley) investigates his home. In the original graphic novel, the only thing seen in the closet was his costume, a MAC-10, and a few knives.
Cobray CM203 Flare Launcher
A Cobray CM203 Flare Launcher is seen in The Comedian's (Jeffrey Dean Morgan) hidden closet armory, standing in for the HE-grenade launcher M203 grenade launcher. Aside from the error that this weapon is recognized as standing in for a destructive device, this is also the newer model CM203 (not released in 1985), so it is anachronistic as well.
M60 Machine Gun
An M60 machine gun is seen used by one of the US soldiers in Vietnam (Director's Cut only), and one is also seen in The Comedian's (Jeffrey Dean Morgan) hidden closet armory.
Smith & Wesson Model 10 revolvers are used by the guards in Riker's prison, one of which is taken by Silk Spectre II (Malin Akerman) and later used to shoot Adrian Veidt (Matthew Goode), who impressively catches the bullet. They are also carried by some of the NYPD police.
A Smith & Wesson Model 586 with a four inch barrel is used by Roy Chess (Douglas Chapman) to fire at Adrian Veidt (Matthew Goode) and shoot three employees (killing two) before Veidt hits him with a pole. In the novel the gun was a Beretta Cheetah modeled gun.
Walther PPK
A Walther PPK is left at Moloch's (Matt Frewer) side after he is murdered in which we see the person planting it unscrews the suppressor and places it next to him. Rorschach (Jackie Earle Haley) later finds it when he comes to ask Moloch questions, finding himself trapped by the police and framed for the murder.
Colt Detective Special
When Daniel Dreiberg (Patrick Wilson) and Laurie Juspeczyk (Malin Akerman) fight off "Knot-Tops" in the alleyway, one of them draws a Colt Detective Special and fires several shots at Laurie but only succeeds in shooting one of his comrades in the back and is dispatched by Dan.
Colt Police Positive Target
A Colt Police Positive Target is seen drawn by Gerald Grice, the man who murdered the little girl Blair Roche, when he enters his house, but he is quickly disarmed by Rorschach (Jackie Earle Haley).
Glock 17
Police standing behind Adrian Veidt (Matthew Goode) as he attempts to stop Roy Chess (Douglas Chapman) from swallowing a poison capsule are armed with Glock 17 pistols, which were not in police service in 1985 (although commonly are today). An even worse error is the fact that they are 2nd Generation G17s, when only the 1st Generations were available in 1985.
M1 Garand
During the opening sequence summing up the past, Hippies stick flowers into US Army Military Policemen's M1 Garand rifles before the MPs fire them on the hippies, flowers still in the muzzles. This is an homage to the famous photograph where a protestor places a flower in the barrel of an MP's M14 rifle. In reality, MPs in the U.S. did use M14 Rifles during this time period. National Guardsmen (as in the Kent State shooting in 1970) were armed with M1 Garands.
Specifically designed by Nite Owl II/Daniel Dreiberg (Patrick Wilson) for him, Rorschach (Jackie Earle Haley) uses this grapple gun to enter Edward Blake's (Jeffrey Dean Morgan) apartment and later uses it as a weapon to break a SWAT member's collar bone.