from: http://callofduty.filefront.com/info/Weapons_US_M1Carbine
The M1 Carbine was designed to meet the needs of soldiers who needed to carry a lighter load (i.e. paratroopers, truck drivers, and other vehicle operators), and those who needed a weapon that could fill the gap between the heavier, bulkier, M1 Garand and their M1911A1 .45 sidearm pistol. The M1 was said to be much more effective at nearly any range except point-blank, which was better suited for the .45 pistol. The least favorite of features voiced by soldiers on the M1 was it’s lack of windage adjustment on the “leaf like” sight of the rifle. The weapon originally used selective fire methods, but after WWII, the newer M2 Carbines fired on automatic, with selective trigger groups removed. The M2 also had a larger, 30 round magazine as compared to the 15 round box magazine of the M1.
The M1 Garand was the weapon of choice for infantry. The M1 Carbine, half the weight and with a less powerful cartridge, was the weapon of choice for support troops, and others not primarily involved in infantry combat. It was designed to meet combat needs less demanding than the M1 Rifle, but more than can be met by the M1911A1 pistol. It was more convenient to use than the M1, and less intrusive to their other duties, while still much more effective than hand guns.
Originally, the M1 was to be capable of selective fire control, but this was dropped. Because a demand arose for an automatic capability, the M2 was developed, with a selective-fire switch added to the left side of the receiver, operating on the sear mechanism.
The US Carbine, Caliber .30in, M3, or T3, was simply an M2 with suitable mountings prepared on the receiver to take various models of infra-red night-sighting devices. No open or conventional sights were provided, and the IR carbine mounted an M3 flash hider, a simpler design than that for the M1C Garand. The M3 carbine, (its development title was T3), was produced in limited numbers as a semi-prototype. Only about 2100 were manufactured compared to 5,510,000 M1 carbines, 150,000 M1A1 carbines and 570,000 M2 carbines.
The M1 and M2 Carbines were also much more powerful than the Russian type burp guns used by the North Koreans and, later, the Chinese, having more than twice their muzzle energy.
In the infantry, the M2 Carbine was carried by Staff NCOs and officers. With its 30 round magazine, rapid fire and greater stopping power, it was an effective counter to the various submachine guns used by the Communists in the Korean War.
In intense cold, however, such as the Chosin battle, light weapons such as the carbine and air-cooled .30 calibre light machine guns malfunctioned much more often than the M1 and the water-cooled heavies, with anti-freeze in their jackets. The Marines used alcohol based hair tonic as anti-freeze lubricants for all light weapons, with good success, but the carbine components were small and fragile, and repeatedly malfunctioned.
The Carbine continued to be used in Viet Nam, until replaced by the M16.