The U.S. Marine Corps has adopted the SOCOM version of their M32 40mm “revolver” grenade launcher as the M32a1. Six shot, "revolver" type 40mm grenade launchers have been around for years. But the U.S. military never adopted them until 2006 when marines in Iraq got some. Originally known as the MGL-140 and used by police and military organizations for years this 40mm, six shot grenade launcher was renamed the M32.
This weapon is, literally, a shotgun size revolver that fires standard American 40mm grenades. Thus it has a minimum range of 30 meters, and a maximum range of 400 meters. The weapon is 81.3cm (32 inches) long, and weighs six kg (13.2 pounds) empty, and 9.2 kg (20.3 pounds) loaded. The 40mm rounds weigh about .54 kg (19 ounces) each.) Like any 40mm grenade launcher, it can fire lethal and non-lethal (tear gas, Etc.) rounds, and fire all six of them in a few seconds. The M32 also has a rail for mounting various types of aiming devices (day and night scopes). The M32s cost about $6,000. Eventually each marine battalion received up to several dozen M32s, depending on what kind of operations the unit was involved in.
Marines and soldiers have used their single shot, 40mm grenade launchers, a lot since 2001, and with much success. The single shot 40mm launchers have been around since the 1960s, and the marines wanted to try something new. The U.S. Navy SEAL commandos (which are part of SOCOM) noted the M32 and by 2011 had in service a customized version called the Mk14. This was the same weight as the M32 but with a shorter (by 10cm to 20cm) barrel. The barrel was stronger, to handle high-powered (and faster) 40mm grenades used in automatic grenade launchers. The Mk41 was more compact (61.3cm/28 inches) long and that made it easier to handle in combat. The marines have now adopted this version as the M32a1.