Mk2 grenade

Mk 2 Grenade
World War II-era Mk 2 grenade
Type	Time-fused grenade
Place of origin	United States
Service history
In service	1918–1960s
Used by	Argentina, Brazil, Chile, Israel, Italy, Netherlands, Turkey, Philippines, United States
Wars	World War I, World War II, Korean War, Vietnam War, Suez Crisis, Six Day War
Production history
Designer	John Browning
Designed	1918
Produced	1918-1950s
Specifications
Weight	About 1 lb 5 oz (595 g) depending upon filling
Length	3.5 in (89 mm) body 4.5 in (114 mm) overall
Diameter	2.3 in (58 g)
Filling	Varied
Filling weight	Varied
Detonation mechanism	percussion cap & time fuse: 4-5 second delay

The Mk 2 grenade (initially known as the Mk II) is a fragmentation type anti-personnel hand grenade introduced by the U.S. armed forces in 1918. It was the standard issue anti-personnel grenade used during World War II and in later conflicts, including the Vietnam War. Replacing the failed Mk 1 grenade of 1917, it was standardized in 1920 as the Mk II, and redesignated the Mk 2 on April 2, 1945.

The Mk 2 was replaced by the M26-series (M26/M61/M57) and later M33 series (M33/M67). It was phased out gradually in service beginning with the Korean War. Due to the tremendous quantity manufactured during World War 2, it was in limited standard issue with the US Army and US Marine Corps throughout the 1950s and 1960s. The U.S. Navy was one of the last users when it was discontinued in 1969.

The Mk 2 grenade replaced the failed Mk 1 grenade used by the U.S. military during World War I. 44 million were ordered and over 21 million were completed (it was possible to convert Mk 1 grenade bodies to the Mk 2 configuration) before the war ended, but few reached American troops overseas. It was formally standardized in 1920. The Mk 2, like the Mk 1, was manufactured of cast iron with a grooved surface divided into 40 knobs in 5 rows of 8 columns. This was to enhance fragmentation (in practice, it was found that the grooves did not enhance fragmentation as much as desired) and provide a better grip when handling and throwing the grenade. The grooves and knobs gave it the appearance of a pineapple, and are the origin of that nickname. It was also commonly referred to as a "frag" grenade, in contrast to other types of grenades such as the Mk 3 grenade concussion grenade

The Mk 2 used the M5, M6, M10, M11, or M204 series fuses. The early M5, and the later M6 and M204 series detonating fuses, were used on high explosive-filled grenades. The M10 and M11 series igniting fuses were used on low explosive-filled ones. The early fuses had many problems. In the M5, moisture could get in under the foil fuse cap, causing the weapon to fail to detonate. The early fuses were not completely silent and made a loud "bang" and produced sparks when activated. They also made a faint "hissing" sound while burning, potentially alerting the enemy of their presence. The M10, used during the interwar period, and the M10A1, used early in WWII, sometimes prematurely detonated when the flash from the primer hit the explosive charge rather than the delay fuse. They were replaced by the M10A2 and M10A3. A less common type of igniting fuse was the M11.