Mk 2 grenade

The Mk 2 grenade (sometimes written 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 I of 1917, it was standardized in 1920 as the Mk II, and redesignated the Mk 2 in 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.

Description

The Mk II was manufactured with grooves in the cast iron to enhance fragmentation and provide a better grip handling and throwing the grenade. These gave it the appearance of a pineapple and origin of that nickname. It was also commonly referred to as a "frag" grenade, in contrast to the Mk 3 grenade concussion grenade.

The original Mk II grenade had a 3/8-inch threaded plug in its base covering the opening used to place the explosive filling. The improved "Mk IIA1" (a designation used informally by armorers, historians, and collectors but was never officially by the US military^[1]) introduced in 1942 was filled through the fuse well instead.

Low explosive Mk II grenades were filled with smokeless EC powder, which produced an adequate amount of fragmentation and did away with the need of a detonator. It 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.

High Explosive Mk II's used flaked or granular TNT. 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 fuses. 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 the enemy of its presence. 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 fuse cap, causing the weapon to fail to detonate. Improved smokeless and (almost) silent fuses (like the M204-series) were later fitted after World War II.

Variants

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 unfused to prevent accidental detonation. Their fuses were shipped separately and came in flat cardboard boxes of 25. EC Powder grenades were shipped with their fuses attached.

Variants included:

• 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 fuse 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 fuse vents.

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 fuse 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 over-painted 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, often with the end painted light brown indicating a "low explosive" marking charge.

Gallery

• 
  Post World War II-era Mk 2.
• 
  Bottom of a post-1920 / pre-1942 baseplugged Mk 2.
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  HE variant of the Mk 2.
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  M21 Practice variant designed for training.
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  A Vietnam War era Mk 2 grenade.
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  M10A3 series fuse assemblies on a Mk II-A1 grenade, dating from 1942.
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  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, The Netherlands, in 2008.
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  U.S. M10A3 Mk-2 A1 hand grenade 1945 Lot World War II era Mk2 grenade in restoration recovered in Brazil RJ in 2013.
• 
  U.S. M10A3 Mk-2 A1 hand grenade 1945 Lot World War II era Mk2 grenade in restoration recovered in Brazil RJ in 2013.

See also

• M1 Grenade Projection Adapter
• 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

Wikimedia Commons has media related to Mk II grenade.

• Information about the Mk 2 at inert-ord.org