Designed by a team from MIR(c) including Major Millis Jefferis and Stuart Macrae, the grenade consisted of a glass sphere containing an explosive made of nitroglycerin and additives which added stability to the mixture and gave it a squash-head-like effect, where the explosive deformed and spread out on the target before exploding. The detonation would be concentrated on a small area, rupturing a thicker armour plate than a more diffuse explosion. The charge was covered in a strong adhesive and surrounded by a sheet-metal casing.