The Mark II or Mk 2 Fragmentation Grenade was first designed in 1918, as a replacement for the unreliable Mk I grenade. The weapon was the standard issue grenade for US forces in World War II, and was used until it was phased out around the time of the Vietnam War, though some are still in use in Third World countries today. The grenade initially had a TNT charge, but it was found that TNT produced fragments too small to be effective. Because of this, a the TNT version was used as an HE grenade, while a version loaded with EC (smokeless firearm powder), which produced more effective fragments, was issued. The weapon is commonly referred to as a "pineapple grenade" because of the gridded grooves cut into the side, intended at the the time to help with fragmentation, though in truth, they had no such affect.