Mk 18 Mod 0 grenade launcher

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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)
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
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
A Mk 18 grenade launcher in use on a Patrol Craft Fast (on top of the dual .50 M2 Browning machine guns)

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.

Test results[edit]

From results of the evaluation it was concluded that the prototype 40mm Mk 18 Mod 0 grenade launcher as received from Honeywell Inc. would fire 5,000 rounds without failures caused by parts wear. However, during the evaluation, the performance of the gun, especially during the first 3,000 rounds was unsatisfactory because of the high stoppage rate due to faulty ammunition belting, inadequate firing pin protrusion, and the rough cycling action of the weapon at higher rates of fire. It was also recommended that the firing mechanism be modified to prevent inadvertent firing of the round during movement of the firing pin from the safe to fire position.

While this concept was soon declared obsolete due to the introduction of the Mk 19 grenade launcher, more than 500 of the new weapons had been ordered by the US Navy from Honeywell, Inc, which developed the weapon in 1963, under contracts of more than $750,000. Designed for use on a low tripod, the small lightweight weapon is capable of firing up to 375 meters at a rate of over 250 rounds a minute. For its naval role, the gun was expected to be mounted atop a .50 caliber machine gun on the stern of each Patrol Boat, River. Two rounds are fired during each full crank revolution with loading occurring at the 3 and 9 o'clock positions of the crank, and firing at 6 and 12. A three position knob is located at the rear of the gun for "fire", " safe," and "load" control. For the Navy, a 48-round ammo box weighing 35 lbs. was used. A 19-lb 24-round box was available for use in the field. Belts were hand-loaded and could reused up to five times.

The Mark 18 was used primarily on small boats or in fixed positions such as bunkers; their primary users were the so-called “river rats” and the SEALs. They could be mounted on M2HB, M60, M1919 tripods, or pintle mounts, but could not be fired without such a mount.

A Mk 18 grenade launcher (upper) displayed at Hanoi Weaponry Museum

See also[edit]