Grease Gun

The M3 "Grease Gun" submachine gun is a submachine gun firing a .45 ACP round common to both the Colt M1911 and M1 Thompson Submachine gun. The M3 was made as an alternative to the more expensive M1 Thompson. The M3 was made entirely out of stamped and welded steel, much like the Sten SMG. The M3 had a slower rate of fire, allowing for the SMG to be a bit more accurate than the Thompson. The weapon is commonly nicknamed the "grease gun," owing to its similarity in appearance to the common mechanic's tool. It also served vehicle and tank personel well due to its compact size and ease of use in tight quarters. The M3 also came with an adapter to convert it to fire 9x19MM Luger/Parabellum, another feature it shared with the Sten. Despite its advantages, many infantry troops in the European Theater preferred the firepower and durability of the Thompson. The M3 found a better place in the Pacific, where the USMC, at the time being the most undersupplied force in the US Military, didn't have access to the Thompson. The M3 was used well beyond WW2, seeing action in Korea, Vietnam and even used by some units in the U.S Army up to Operation Desert Storm until finally being replaced with the M4 Carbine. The "Grease Gun" is not a very common weapon in the Call of Duty series.

Call of Duty: Finest Hour
The M3 is featured in one mission only, in the mission you play as Sergeant Sam Rivers in an American Sherman Tank. While on foot the player receives an M3. The Grease gun has a slightly larger sight than the Call of duty 2 model and has a faster firing rate. However it lacks in power, but overall a good choice of weaponry for the mission.

Call of Duty 2
In Call of Duty 2, the Grease Gun is a copy of the Thompson from Call of Duty 1 with a few differences. It has 32 rounds in its magazine, very manageable recoil, good damage, and good accuracy. However, it has a very low rate of fire, making it harder to effectively use it in close quarters, especially when up against a faster weapon. It's sights are also very small (it's just a tiny triangle-shaped pin at the gun's front), making it difficult to get accurate shots. Nonetheless, it's a solid weapon that users of the CoD1 Thompson might prefer over the CoD2 Thompson, or for those looking for a change.