mk2 grenade
A fragmentation-type anti-personnel hand grenade introduced by the United States military in 1918. It was the standard issue anti-personnel grenade used during World War II, and also saw limited service in later conflicts, including the Korean War and Vietnam War. It replaced the failed Mk 1 grenade of 1917. The grooves and knobs gave the Mk 2 appearance of a pineapple, and are the origin of the nickname.
It was gradually phased out of service as the M26-series grenade was introduced during the Korean War. Due to the tremendous quantity manufactured during WWII, the Mk 2 was still in limited issue with the US Army and US Marine Corps throughout the 1950s and 1960s.