Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A recoilless gun or recoilless rifle (RCLR) is a lightweight weapon that fires a heavier projectile that would be impractical to fire from a recoiling weapon of comparable size. Technically, only devices that use a rifled barrel are recoilless rifles. Smoothbore variants are recoilless guns. This distinction is often lost, and both are often called recoilless rifles. Normally used for anti-tank roles, the first effective system of this kind was developed during World War II by William Kroeger and Clarence Musser.