It was named the "Pineapple Grenade" because of the ridges and its shape. It has these ridges for fragmentation purposes. With a body made of cast iron, the first grenades were often filled with black powder, and had a detonation time of around 5.2 seconds.
To arm the grenade, one must hold down the striker lever which is on the side of the grenade and pull out the safety pin. By doing this the grenade will begin its detonation countdown once the grenade is thrown and the lever is no longer depressed.
Originally, the safety pin was what was holding the lever in place, but without the pin, the user is what is holding the lever against the body. When the lever becomes no longer depressed, the striker is allowed to hit a percussion cap which starts the chemical countdown for detonation.
Although, the Mk II had very little official variants, over time, the design was changed and modified. These were usually minor changes such as in the late 1930s the shape of the grenade was changed ever so slightly and at this time, the HE version of the grenade (there were other versions such as smoke) was painted bright yellow and so in 1942 came the pain change to olive drab. One of the official variants was the Mk IIA1 which like the first Mk II had a black powder filler and had a new fuse. The Grenade, Hand, Fragmentation, HE, Mk II had a TNT filler and a new M5 fuse while the Grenade, Hand, TNT, Fragmentation, Mk II also had a TNT filler and a different fuse.
The Mk II was even capable of being equipped with a special stabilizer so that it could be fired as a rifle grenade. The stabilizer was attached via three prongs on the top of the stabilizer and to arm the pin is removed, since the lever is being supported by one of the prongs, it is safe to fire.
The Mk II was designed in 1918 and was used in the latter days of the First World War in limited numbers. The earlier Mk I Hand Grenade was soon replaced by the much improved Mk II, and by 1918, it was all but gone from US service. By 1941, the Mk II was the United States' main hand grenade and it was used throughout World War II by US forces. In 1945, it was resignated the Mk 2 Hand Grenade. The Mk II was later used in the Korean War, where it was supplemented by the M26 fragmentation grenade, and the Vietnam War, during which it was entirely replaced by the M67 grenade.