Mk 18 Mod 0 grenade launcher

Mk 18 Mod 0 grenade launcher
Mk 18 Mod 0 grenade launchers (right and on tripod) at the War Remnants Museum (Ho Chi Minh City)
Type	Grenade launcher
Place of origin	United States
Service history
In service	1960s - Early 1970s
Used by	United States Navy
Wars	Vietnam War
Production history
Manufacturer	Honeywell Corporation and Aeronautical Products Division
No. built	1200
Specifications
Crew	2
Cartridge	40 x 46 mm grenade
Caliber	40mm
Barrels	1
Action	Hand cranked, manual reloading
Rate of fire	250 rounds per minute
Effective firing range	2200 yards
Feed system	Belt
Sights	Iron sights

The Mk 18 Mod 0 was a 40x46mm grenade launcher used by the United States Navy during the Vietnam War and also the last known hand crank operated firearm since the Gatling gun. It was replaced by the Mk 19 grenade launcher in service with the United States Armed Forces.

This weapon is a manually-operated, belt-fed, rapid-fire 40mm grenade launcher designed to attack targets with high explosive fragmenting grenades. It will fire at variable rates up to 250 rounds per minute at ranges from approximately 328 yards to 2,200 yards. The rotary split breech, utilized in this weapon, allows straight through feeding of ammunition and eliminates the need for a reciprocating bolt, extraction of ammunition from a belt, extraction from a chamber and ejection for the weapon.The 40mm Mk 18 utilizes a split breech concept which has been previously used but has some original characteristics based on the introduction of a mechanism to allow the top rotor to move vertically and synchronizes the bottom rotor. Between 1965 and 1968, approximately 1200 of the Mk 18 Mod 0, 40mm multiple grenade launchers were produced by the Honeywell Corporation and Aeronautical Products Division, Hopkins, Minnesota.

The first patent application was filed by Honeywell in 1964, however, the initial development work commenced in late 1962. The concept was originally proposed during a study on the behavior of fuzes for the M79 grenade launcher's ammunition. Honeywell had anticipated the need for a simple, inexpensive, and extremely mobile rapid-fire weapon that could provide a team of two with an effective means of delivering large quantities of explosive grenades within a limited range primarily for suppressive and defensive fire purposes. The development of the 40mm grenade with its high–low system made such a weapon possible by permitting the use of a split breech mechanism which allowed the weapon to be extremely light and simple.