The Ordnance ML 4.2-inch mortar was a heavy mortar used by the British Army during and after World War II.
The mortar was a smooth-bore weapon of the Stokes pattern and was designed by the Armaments Research and Development Establishment and produced by the Royal Ordnance Factories. It entered widespread British service in 1942, equipping chemical warfare companies of the Royal Engineers (RE). The Mark 3 became the standard model.
The first combat use was at Second Battle of El Alamein, when the 66th Mortar Company (RE) was attached to the Australian 24th Infantry Brigade. During the battle, 66 Mortar Company provided intense, effective supporting fire on the 24th Brigade's exposed right flank, as the infantry advanced, expending all of the 4.2-inch HE mortar ammunition in the theatre.
Around mid-1943, the Royal Engineer chemical warfare companies were disbanded as an emergency expedient and one heavy mortar company of each infantry division machine-gun battali