Question: What weapon was used most by the Allied forces in World War II?

List of World War II weapons of the United States

Below are lots of different types of weapons used in World War II by the United States. 
Small arms
Pistols (manual and semi-automatic)
Colt M1911A1
Colt Model 1903
Colt New Service
Colt/S&W M1917 revolver
Colt Official Police (Colt M1927 Aka "Colt Commando")
FP-45 Liberator (Dropped into occupied territories for use by insurgents)
Smith & Wesson M&P
Submachine Guns
Thompson submachine gun (.45 ACP)
M3 submachine gun (.45 ACP)
M50 Reising submachine gun (.45 ACP)
United Defense M42 (9x19mm Parabellum)
Rifles
M1903 Springfield (.30-'06)
M1 Garand (.30-'06)
M1917 Enfield rifle (.30-'06)
M1941 Johnson rifle (.30-'06)
M1 and M1A1 carbine.
Marlin Model 1894
Winchester Model 1894
Winchester Model 1895
Shotguns
Winchester M1897
Winchester M12
Browning Auto-5
Remington 31
Stevens M520-30
Ithaca 37
Grenades and grenade launchers
M7 grenade launcher
Mk 2 grenade
Mines
M1 mine
M5 mine
M7 mine
Recoilless rifles
M18 recoilless rifle
M20 recoilless rifle
Flamethrowers
M1A1 flamethrower
M2-A1 flamethrower
Ronson flamethrower
Butane torch
Infantry and dual-purpose machine guns
Lewis Gun
Browning M1917A1 (.30-'06)
Browning M1918A2
Browning M1919A4/A6 and family (.30-'06)
M1941 Johnson Light Machine Gun (LMG) (.30-'06)
Browning M2HB (.50 BMG)
Vehicle and aircraft machine guns and autocannons
M4 cannon
M2 cannon
50 caliber  machine gun (Browning M2)
M1919 Browning machine gun
Blades
M1 bayonet
M1917 bayonet
M4 bayonet
Ka-bar
Bolo knife
Bowie knife
United States Marine Raider stiletto
Tanks
M2 Light tank
M2 Medium Tank
M3 Stuart[1]
M5 Stuart
M22 Locust
M24 Chaffee
M3 Lee
M4 Sherman
M26 Pershing
M6 (Prototype)
T29 (Prototype)
T30 (Prototype)
T32 (Prototype)
LVT-1 alligator
M10 Tank Destroyer
M18 Hellcat
M36 Tank Destroyer
Artillery
Infantry mortars
M1 Mortar
M2 4.2 inch mortar
M2 Mortar
Heavy mortars & rocket launchers
T34 Calliope
T40 Whizbang
Self propelled guns
Howitzer Motor Carriage M8
M40 Gun Motor Carriage
M7 Priest
Field artillery
75 mm Gun M1917 - copy of British gun re-chambered for French cartridge, produced for export
QF 2.95-inch Mountain Gun  - imported from Britain, used in Philippines
75 mm Gun M2/M3/M6
M116 howitzer (75mm) -also known as "75mm Pack Howitzer M1"
76 mm gun M1
M101 howitzer (105mm) - still used in US and worldwide as late as in 2014
M3 howitzer (105mm)
Canon de 155mm GPF
M114 155 mm howitzer - also known as M1 155mm Howitzer
M2 155 mm Field Gun (Long Tom)
4.5-inch Gun M1 - version to fire British ammunition
M115 203 mm howitzer
8-inch Gun M1
M1 240 mm Howitzer
Fortress and siege guns
5"/51 caliber gun (coastal defense)
8-inch M1888 (obsolete)
8-inch Mk. VI railway gun
M1918 240 mm howitzer (obsolete)
8-inch Mk. VI railway gun
12-inch coast defense mortar (also railway version)
12-inch Gun M1895
14-inch M1920 railway gun
16"/50 caliber M1919 gun
Anti-tank guns
National Forge & Ordnance 37mm gun (1941) - export (to Dutch) only
M3 37 mm Anti-Tank Gun
M1 57 mm Anti-Tank Gun
M5 3-Inch Anti-Tank Gun
105mm Gun T8 AT/AA gun (cancelled)
Anti-tank weapons (besides anti-tank guns)
Rocket Launcher M1/M1A1/M9 (Bazooka)
Boys anti-tank rifle
M18 Recoilless Rifle
M20 recoilless rifle
See also
List of U.S. Army weapons by supply catalog designation
List of individual weapons of the U.S. Armed Forces
List of crew-served weapons of the U.S. Armed Forces
List of vehicles of the U.S. Armed Forces
American Military Technology During World War II
List of World War II weapons