Mk 2 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, Suez Crisis, Six Day War
Production history
Designed	1918
Specifications
Weight	1 lb 5 oz [595 grams]
Length	3 5/6" [111mm]
length	2 5/16" [59mm]
Filling	TNT or EC blank fire powder
Filling weight	2 oz
Detonation mechanism	percussion cap & time fuse: 5 second delay

The Mk 2 defensive hand grenade (sometimes written Mk II) is a fragmentation hand grenade used by the U.S. armed forces during World War II and in later conflicts including the Vietnam War. The Mk II was introduced in 1918, replacing the failed Mk I of 1917, and was standardized in 1920. On 2 April 1945 the Mk II was redesignated the Mk 2.

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 the 1970s.

Description

The Mk II was manufactured with grooves in the cast iron. This was to allow fragmentation and also provided a better grip when throwing the grenade. This gave it the appearance of a pineapple fruit, giving it the common nickname of the "pineapple" grenade. It was also commonly referred to as a "frag" grenade - as opposed to the Mk.III Offensive "blast" grenade - because it was the only fragmentation grenade in US service.

The original Mk II grenade had a 3/8" threaded baseplug in its base. This was designed to place the explosive filling. The product-improved "Mk IIA1" introduced in 1942 lacked the bottom filler hole of the Mk II and was filled through the fuse well. (Note: The term "Mk. IIA1" is used informally by armorers, historians, and collectors but was never officially used as a nomenclature by the US military.)

Mk. II grenades were filled with EC blank fire (smokeless firearm) powder. It produced an adequate amount of fragmentation and did away with the need of a detonator. The detonator was initially replaced by a small length of safety fuse terminated with a black powder igniter charge. Production grenades with the EC powder filler used the M10 series of igniting fuse.

TNT was used in some Mk. II models but it had a tendency to over-fragment the cast iron body. Pre-war Mk. IIs with a TNT filler were identified with an all-yellow body as a warning to users. Wartime grenades were repainted olive drab for camouflage purposes with a narrow yellow band below the fuse. Repainted grenades usually lacked the yellow band.

The Mk. II used the M5, M6, and M10 series fuzes. These early fuses made a loud "bang" and produced sparks when activated. They had other problems as well. The M10-series' powder train made a "hissing" sound as it burned, potentially alerting enemy targets. The M5 and M6 series sometimes prematurely detonated when the flash from the primer hit the TNT charge rather than the delay fuse. Moisture could get in under the foil fuze cap, causing the weapon to fail to detonate. Improved smokeless and (almost) silent fuses (like the M204-series) were later fitted after World War 2.

M1 Grenade Adapter

The Mk 2 can also be used as a rifle-grenade when attached to the M1 Grenade Adapter, an add-on 22mm stabilizer tube and fins. The user pulled the Mk.2 grenade's pin and inserted it into the prongs; a holder kept the arming lever from releasing. He then loaded and fired the rifle grenade from the M7 grenade launcher. Inertia causes the holder to shear off in flight, releasing the lever and arming the grenade. The M1 Grenade Adapter supplemented and eventually replaced the M17 Fragmentation rifle grenade by mid-1944.

• M1 = 4 prongs, no base cup, and solid or slotted tailfins.
• M1A1 = 3 prongs, base cup to secure the grenade, and solid tailfins.
• M1A2 = 3 prongs, base cup to secure the grenade, and slotted tailfins.

Variants

• Grenade, Hand, Fragmentation, Mk II: EC powder filler, uses M11 or M10A1 igniting fuse.
• Grenade, Hand, Fragmentation, Mk IIA1: EC powder filler, uses M10A2 igniting fuse. Has no baseplug because it was filled through the fuze well.
• Grenade, Hand, Fragmentation, HE, Mk II: TNT filler, uses M5 detonating fuse.
• Grenade, Hand, TNT, Fragmentation, Mk II: TNT filler, uses M6A4C detonating fuse.
• Grenade, Hand, Practice, Mk II: Black Powder "spotting" charge in a cardboard tube connected to a M10-series igniting fuse. Has a standard body with a wooden or cork baseplug that popped out during detonation, creating a loud report (i.e., "BANG" noise) and smoke to indicate ignition. The body would be reused and reloaded as long as it remained intact.
• Grenade, Hand, Practice, M21: Black Powder "spotting" charge, uses M10-series igniting fuse. Has a heavier body and no baseplug. Its body was embossed with the vertical letters "R" "D" and "X" on the knobs in a column on one side (because it was originally designed to be for an HE grenade with a more powerful RDX filler). When detonated, it made a loud report and smoke came out of the fuze vents.

Mk. II Grenades came 25 to a wooden crate and were shipped in fiberboard packing tubes. TNT grenades, like all High Explosive devices, were shipped unfuzed to prevent premature detonation. Their fuzes were shipped separately and came in flat cardboard boxes of 25. EC Powder grenades were shipped with their fuses attached.

Specifications

• Body: Made of cast-iron with a grooved surface that is divided into 40 knobbed segments in 5 rows of 8 columns. Models made from 1918 to 1942 have a 3/4"-threaded baseplug to insert or remove the explosive filler. Models made from 1942 onwards were filled through the fuze well to speed up production.
• Fuse: Dependent on variant, includes M5 and M6 detonating fuses (for Mk.2s with a High Explosive filler), and M10 igniting fuses (for Mk.2s with an EC Black Powder filler). The delay time was 4 to 5 seconds.
• Charge: Either a Low Explosive (EC powder) or High Explosive (flaked or granular TNT) filler.
• Markings: Low Explosive grenades were made of blackened iron or were painted Gray or Black to prevent rust. Pre-war High Explosive grenades were painted Yellow; wartime grenades (c.1942 and onward) were overpainted or painted Olive Drab with a Yellow ring at the top. Mk. II Practice grenades (c.1920-1945) were painted Red (a practice copied from the French military). M21 Practice grenades (c.1945 to 1950s) were painted light Blue (a practice copied from the British military) and had blue-painted fuse levers.

Gallery

• 

  Post World War II-era Mk 2.

• 

  Bottom of a post-1920 / pre-1942 baseplugged Mk 2.

• 

  HE variant of the Mk 2.

• 

  M21 Practice variant designed for training.

• 

  A Vietnam era Mk 2 grenade.

• 

  M10A3 series fuse assembly's on a Mk II-A1 grenade, dating from 1942.

• 

  Note: the early Mk. II grenade (with baseplug) with M1 Grenade Adapter (1st from left) and Mk. IIA1 HE grenade (without baseplug) warhead on the M17 Rifle Grenade (3rd from left).

• 

  A World War II era Mk2 grenade recovered in Opheusden in 2008.

• 

  U.S. M10A3 Mk-2 A1 defensive hand grenade 1945 Lot World War II era Mk2 grenade in restoration recovered in Brazil RJ in 2013.

• 

  U.S. M10A3 Mk-2 A1 defensive hand grenade 1945 Lot World War II era Mk2 grenade in restoration recovered in Brazil RJ in 2013.

See also

• United States hand grenades

Notes and references

• Gervasi, Tom. Arsenal of Democracy II: American Military Power in the 1980s and the Origins of the New Cold War: with a Survey of American Weapons and Arms Exports. New York: Grove Press, 1981. ISBN 0-394-17662-6.
• War Department. Field Manual FM 23-30-1944 Hand and Rifle Grenades; Rocket, AT, HE, 2.36" (February, 1944); pgs. 5-6.

External links

• Information about the Mk 2 at inert-ord.org
• Film of detonating Mk2 grenade — 2/3 million frames per second