Meanwhile, the British No. 68 AT rifle grenade was proving to be too light to deal significant damage, resulting in it rarely being used in action. Due to these limits, a new infantry anti-tank weapon was needed, and this ultimately came in the form of the "projector, infantry, anti-tank" or PIAT. By 1942, the PIAT had been developed by Major Millis Jefferis. It was a combination of a HEAT warhead with a spigot mortar delivery system. While cumbersome, the weapon allowed British infantry to engage armor at range for the first time. The earlier magnetic hand-mines and grenades required them to approach dangerously near. During World War II the British referred to the Monroe effect as the "cavity effect on explosives".