One of the most recognizable weapons in history, the Thompson even gained a nick-name that took on a generic meaning to describe any sub-machine gun: the Tommy Gun.
The Thompson Sub-machine gun was designed by General John T. Thompson in 1921 in response to a combat lesson learned during the First World War. High volume of fire is needed in close-quarter combat. The M1 first saw combat in limited quantities in the hands of U.S. Marines, such as Chesty Puller in Nicaragua in 1927. The “Tommy” was the only allied submachine gun in mass production at the beginning of WWII. I The .45 cal round gives the Thompson tremendous stopping power. Paratroopers commonly used a 20-round magazine. The pictured Thompson M1A1 employs the more common 30-round magazine.
The M1 Thompson had several weaknesses; e.g. weight and control. It's rate of fire made control difficult. And the weapon is expensive to manufacture.
U.S. M-3 Submachine Gun
Designed as a replacement for the Thompson submachine gun, the M-3 was officially adopted on December 24, 1942. It quickly earned the nickname "grease gun" for its resemblance to the tool used to grease cars. The weapon was crude in appearance and had a simple finish, however, its looks concealed a simple but effective blowback operation and a magazine that held 30 .45 caliber rounds. The .45 caliber M3/M3A1 are far easier to manufacture than the Thompson, and have a number of excellent design features in addition. The low cyclical rate of fire makes the gun easier to control than most submachine guns, not only the Thompson. The weapon's straight line of recoil thrust also adds substantially in controlling the gun in automatic fire. The gun's loose tolerances allow for reliable operation even if very dirty and, with its bolt and guide rod design make it more reliable than the Thompson under adverse conditions.