The MK3 offensive hand grenade is a cylindrical concussion grenade designed to produce casualties during close combat while minimizing danger to friendly personnel exposed in the open owing to minimal fragmentation. There is a secondary fragmentation hazard though from rocks, gravel, wood splinters, glass, etc. The grenade is also used for concussion effects in enclosed areas, for blasting, or for demolition tasks. The shock waves (overpressure) produced by this grenade when used in enclosed areas are greater than those produced by the fragmentation grenade. It is, therefore, very effective against enemy soldiers located in bunkers, buildings, and fortified areas. It is commonly known as the "concussion" or "demo" (from demolition) grenade.
The first version was created in March, 1918. It was designed to be used during trench assaults to knock out bunkers and clear trenches without producing fragmentation that could injure the user or friendly forces nearby.
There are three variants: the basic MK3, the MK3A1, and the MK3A2. They differ in their construction and the type of fuse used. They were designated Mk III (Roman numbers) prior to 2 April 1945.