When America entered World War II, the standard U.S. military submachine gun was the famous Thompson M1928A1. The downside of the Thompson Submachine Gun—the Tommy gun—was that it was heavy, hard to produce and expensive to produce. Thus, the Army requested a new submachine gun to replace it. The new variant, known as the M3 Grease Gun, offered low cost, could be produced quickly and was simple. However, it still wasn't simple enough and was made even simpler with the introduction of the M3A1. The crank handle on the M3 was taken off and replaced with a finger hole on the side of the bolt for the M3A1, creating less problems for soldiers during combat. The M3A1 saw service during World War II, the Korean War, the Vietnam War, and even up until Operation Desert Storm in the early 1990s. For more on the U.S. M3A1 Grease Gun, watch this "I Have This Old Gun" segment from a recent episode of American Rifleman TV.