Both Sgt. Joe Enders (Nicolas Cage) and Sgt. Pete "Ox" Henderson (Christian Slater) use Colt M1911A1 pistols as their sidearms. One of the mistakes is that the M1911A1 usually have four magazines as extra ammo, not two like in the film.
Submachine Guns
M1928 Thompson
Sgt. Joe Enders (Nicolas Cage) uses an M1928 Thompson fitted with a 50-round drum magazine during the opening battle in the swamps of Guadalcanal.
M1928A1 Thompson
For the rest of the film, Sgt. Joe Enders (Nicolas Cage) uses an M1928A1 Thompson fitted with a 30-round magazine. Sgt. Pete "Ox" Henderson (Christian Slater) also uses an M1928A1.
Shotguns
Winchester Model 1897 "Trench Gun"
Gunnery Sergeant Richard "Gunny" Hjelmstad (Peter Stormare) uses a Winchester Model 1897 "Trench Gun" as his weapon in the film, although he is never seen firing it. In the "Director's Cut", Hjelmstad uses the shotgun during the surprise Japanese attack on the village.
The M1 Garand is the most common weapon of the US Marines. Most notably seen used by Private Milo Pappas (Mark Ruffalo) and Private Thomas Nellie (Martin Henderson).
M1903 Springfield
Some of the Marines use M1903 Springfield rifles during the opening battle in Solomon Islands. USMC indeed fought with them in Guadalcanal, while the US Army was issued with M1 Garands. It should also be noted that M1903 rifles were commonly used alongside M1 Carbines and Garands due to M1 Garand shortages and that a number of front line Marine and U.S. Army units were still using M1903s as infantry rifles (in Asia and Europe) up until the end of the World War II due to the shortage of M1 Garands.
Machine Guns
M1918A2 Browning Automatic Rifle
Private Charles "Chick" Clusters (Noah Emmerich) uses an M1918A2 Browning Automatic Rifle as his role of the support gunner in the film, although his BAR is firing on the faster auto fire rate and has the bipod removed, suggesting it is used more in the assault rifle role.
Browning M1919A4
Browning M1919A4 machine guns are seen mounted on M2 tripods, pintle-mounted on US jeeps, in a coaxial mount on M4 Sherman tanks as well as in the hands of the US infantry.
Browning M2HB
Browning M2HB machine guns are mounted on M4 Sherman tanks.
Others
M1A1 Bazooka
An M1A1 Bazooka is used by Marines during the battle of Saipan. When two Marines are attempting to take out a bunker with the launcher, the loader is wounded and the gunner is killed, so Sgt. Pete "Ox" Henderson (Christian Slater) runs out and does a stylish "judo-roll", grabbing the launcher in the process. The wounded loader gets back up and readies the weapon, and Ox takes out the bunker single-handedly. Some other Marines are also seen carrying this weapon.
M2-2 Flamethrower
Private Andrew Harrigan (Brian Van Holt) uses an M2-2 Flamethrower as his weapon in the film. True to Hollywood Pvt. Harrigan's M2-2 Flamethrower explodes due to a single shot from an FMJ, engulfing the Private in fire and forcing Sgt. Joe Enders (Nicolas Cage) helps him out of his misery with his pistol. In reality, the fuel inside a flamethrower is often difficult to ignite, which is why built-in magnesium igniters are used. The gas used to pressurize the tanks is also non-flammable. In real life, a hit from an FMJ or lead round would most likely knock the operator off of his feet due to the massive pressure released from the small entrance hole. Although it should be noted that had incendiary ammunition been used there is a chance of an ignition of the tank/operator.
Unknown Smoke Grenade
Marines throw unknown smoke grenades to cover the approach of Sgt. Joe Enders (Nicolas Cage) when he charges a Japanese bunker to throw a satchel charge inside.
A Japanese soldier tries to draw his Nambu Type 14 from his holster before Pvt. Ben Yahzee (Adam Beach) stabs him with the Type 30 bayonet of his captured Arisaka Type 99 rifle.
Rifles
Arisaka Sniper Rifle
While not closely seen, a Japanese sniper takes out a few Marines with an Arisaka rifle, assumed to be a scoped model to fit the sniper role. But due to John Woo logic, he is no match for Sgt. Joe Enders (Nicolas Cage) and a quick hip fire burst from his Thompson.
Arisaka Type 99
The Arisaka Type 99 is the most common weapon of the Imperial Japanese Army. The early models contained a folding wire monopod, flip up sights with "anti-aircraft" bars, chrome-plated bores, and a dust cover. As the war went on, the quality had dropped, these late war rifles were known as "last ditch" rifles and were very crudely manufactured with most missing the accessories of the earlier models.
At one point in the film, Pvt. Ben Yahzee (Adam Beach) disguises himself as a Japanese soldier to acquire a radio after his destroyed, he also takes a substitute standard ("last ditch") Arisaka Type 99 along with the disguise.
Japanese soldiers are seen mowing down Marines with Type 99 Light Machine Guns. While trying to steal a Japanese radio, Sgt. Joe Enders (Nicolas Cage) uses two Type 99s to cover Yahzee as he calls in. Some Type 99s have 20-round magazines.
Others
Type 3 Mine
Type 97 Hand Grenade
Japanese soldiers use Type 97 hand grenades during the opening battle in Guadalcanal. One of the grenades cripples Sgt. Joe Enders (Nicolas Cage) and damages his ear.
Type 89 "Knee Mortar"
Type 89 "Knee Mortars" are used by Japanese soldiers during the unexpected assault on the Marines in the controlled village.
7.7cm Feldkanone 96 n. A.
During the landing on Saipan, Japanese soldiers are seen with a German 7.7cm Feldkanone 96 n. A. While a tad odd to be used by the Japanese, it could be a leftover from the German colonial occupation or as a stand-in for a Type 38 75mm cannon.
Type 41 75mm Mountain Gun
A Type 41 75mm mountain gun is briefly seen next to the Feldkanone.
Type 96 15cm Howitzer
The Type 96 15cm Howitzer is used by Japanese troops.
Type 45 240mm Howitzer
Japanese soldiers use a fixed Type 45 240mm howitzer to ambush an American convoy.