4.2-in Mortar is a British Artillery unit.
Ordnance ML 4.2 inch Mortar is a British heavy mortar that was developed from the Stokes Mortar and was designed by the Armaments Research and Development Establishment and produced by the Royal Ordnance Factories. Ordnance ML 4.2 inch Mortar entered service in 1942 with Royal Engineer chemical warfare companies. These companies were replaced by Heavy Mortar Company of the Divisional Machine-gun battalion for example 1st Battalion, Middlesex Regiment had a Heavy Mortar Company. The Independent Machine-gun Company that served in Armored Divisions also had a Heavy Mortar Platoon.