Ordnance ML 4.2 inch Mortar

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Ordnance SB 4.2 inch Mortar
Ordnance ML 4.2 inch Mortar on mobile baseplate
Type Mortar
Place of origin United Kingdom
Service history
In service 1942-
Used by  United Kingdom
Wars Second World War
Korean War
Production history
Number built about 3,800[1]
  • Barrel: Mk 2 92 lbs
  • Tripod & mounting: 112 lbs
  • Base plate: No 2 baseplate 120 lbs, with auxiliary baseplate fitted 318 lbs, mobile baseplate 602 lbs
Barrel length Mk 1 64 inches, Mk 2 68 inches

Calibre 4.2 inch (106.7 mm)[2][3]
Elevation 45° - 80°
Traverse 10°
Rate of fire 20 rounds for 1 minute, 15 for 3 minutes, 10 for sustained fire
Maximum firing range 4,100 yards (3,750 m)

The Ordnance ML 4.2 inch Mortar was a heavy mortar used by the British Army during World War II, and by other armies postwar.


The 4.2 inch mortar was a Smooth Bore (SB) weapon of the Stokes pattern and was designed by the Armaments Research and Development Establishment and produced by the Royal Ordnance Factories.[4]

It entered British service in 1942, where it was used to equip Royal Engineer chemical warfare companies. The Mark 3 became the standard model. The first combat use was at El Alamein, which expended all the HE ammunition in the theatre.

Around mid 1943, the RE chemical warfare companies were disbanded and one heavy mortar company of each Infantry Division's machine gun battalion was equipped with the mortar. This company was organized with sixteen 4.2-in mortars, divided into four Platoons of four mortars each.

In early 1944, Divisions in Italy also held a pool of mortars for issue to other units as required, usually troops in the divisional anti-tank regiment - some regiments even converted one or more batteries to mortars.

The mortars were somewhat slower in reaching the far east, although the Australian forces in the South West Pacific had them before troops fighting in Burma did.


After World War II, the mortars were handed over to the Royal Artillery - 170 Mortar Battery used them at the Battle of Imjin River in Korea. They were used during the 1950s, including by airborne artillery, deployed to Kuwait in 1961 and manned by soldiers from air defence batteries during the Confrontation in Borneo in 1965.


The 4.2" Mortar entered production at the end of 1941. Initially it was fielded with a standard baseplate and tripod. The normal detachment was 6 men, and it was transported with ammunition in a 10cwt trailer, usually towed behind a Loyd Carrier. There was also an auxiliary baseplate that fitted around it to increase its area for use on softer ground.

Later an integrated trailer / baseplate was developed, called the Mk 1 Mobile Baseplate. The wheels, which were on suspension arms, were unlocked and raised for firing, Mk1/1 had detachable wheels. The barrel with tripod attached was stowed on top for towing. The mobile baseplate trailer mounting could be brought into action by 2 men.[5]


Both HE (9.1 kg) and smoke (10.2 kg) ammunition was used. Smoke include WP and Base Ejection, and in World War II other types for practice.

Two charges were available. In World War II, both streamlined and cylindrical bombs were available.


World War II
  • UK
  • Australia
  • Canada
  • Ethiopia
  • Laos
  • Malaysia
  • Nepal
  • Turkey
  • UK


  1. ^ British Mortars of the Second World War
  2. ^ Brassey’s p. 92
  3. ^ Maintenance Manual for ML 2-inch, ML 3-inch and SB 4.2-inch Mortar
  4. ^ Pugh p. 76
  5. ^ Pugh p. 76


  • Pugh, Stevenson (1962). Fighting Vehicles and Weapons of the Modern British Army (First ed.). London: Macdonald. 
  • Bidwell, Shelford (1977). Artillery of the World (First ed.). London: Brassey’s. ISBN 0-904609-04-9. 
  • Maintenance Manual for ML 2-inch, ML 3-inch and SB 4.2-inch Mortars
  • Bishop, Chris. The Encyclopedia of Weapons of WWII. 

External links[edit]