A recoilless rifle (RCLR) or recoilless gun 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. The key difference to rocket launchers (whether man-portable or not) is that the projectile of the recoilless rifle has no propulsion of its own - once out of the rifle, it does not accelerate further, like a missile or rocket would. 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 Recoilless rifles are capable of firing artillery-type shells at a range and velocity comparable to that of a normal light cannon, although they are typically used to fire larger shells at lower velocities and ranges. The near complete lack of recoil allows some versions to be shoulder-fired, but the majority are mounted on light tripods and are intended to be easily carried by a soldier. A few, such as the British 120mm L4 MoBAT and L6 Wombat could only practically be transported by jeep or truck, or mounted on an armoured personnel carrier.