Based on the Stokes design the first 4.2in mortars were issued in 1942 and first saw service with the Royal Engineers at the battle of El Alamein. In 1943 the 4.2in was used to equip infantry units and were located in machine gun battalions at regimental level. By the end of WW2 the 4.2in had served on every front and continued in service with Royal Artillery units during the Korean War.