ML 4.2-inch mortar

The Ordnance ML 4.2-inch mortar was a British heavy mortar used by the during and after World War II.

Ordnance ML 4.2-inch mortar
Ordnance ML 4.2-inch mortar on mobile baseplate
Place of originUnited Kingdom
Service history
In service1942-present
WarsSecond World War
Korean War
Indonesia–Malaysia confrontation
Indo-Pakistani War of 1965
Production history
No. builtabout 3,800[1]
  • Mk 2 Barrel: 92 lb (42 kg)
  • Tripod: 112 lb (51 kg)
  • No 2 baseplate: 120 lb (54 kg)
  • Auxiliary baseplate: 318 lb (144 kg)
  • Mobile baseplate: 602 lb (273 kg)
Barrel lengthMk 1: 64 in (1.6 m)
Mk 2: 68 in (1.7 m)

Shell weight19 lb 13 oz (9 kg)[2]
Calibre4.2-inch (106.7 mm)[3][4]
Elevation45° - 80°
Rate of fire20 for 1 minute
15 for 3 minutes
10 rpm sustained
Muzzle velocity730 ft/s (223 m/s)[2]
Maximum firing range4,100 yards (3,750 m)


The 4.2-inch (107 mm) 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.[5] 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 Coy provided intense, effective supporting fire on 24 Bde'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 battalion was equipped with the mortar. This company was organized with sixteen 4.2-inch mortars, in 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.

Ordnance ML 4.2-inch mortars were slower to reach Commonwealth forces in the Pacific and Asia. Australian Army units in the South West Pacific theatre were reportedly the first to receive them, before forces in Burma.


After World War II, the mortars were handed over to the Royal Artillery, the 170th Mortar Battery used them at the Battle of Imjin River in Korea. They were used during the 1950s, also 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-inch mortar entered production at the end of 1941 with a standard baseplate and tripod. The normal detachment was six men and it was transported with ammunition in a 10 cwt 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; the Mk1/1 had detachable wheels and 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] Regarding rate of fire, one source reports a crew putting 23 bombs in the air before the first impacted.[6]


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.

Chemical munitions included the MK I chemical mortar bomb with Mustard gas (HS or HT fillings).


World War II

See also

Weapons of comparable role, performance and era


  1. British mortars of the Second World War
  2. Chamberlain, Peter (1975). Mortars and rockets. Gander, Terry. New York: Arco Pub. Co. p. 20. ISBN 0-668-03817-9. OCLC 2067459.
  3. Brassey's p. 92
  4. Maintenance Manual for ML 2-inch, ML 3-inch and SB 4.2-inch mortar
  5. Pugh p. 76
  6. Fendick


  • 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.
  • Horner, David (1995). The Gunners – A History of Australian Artillery (First ed.). St Leonards: Allen & Unwin. ISBN 1-86373-917-3.
  • Maintenance Manual for ML 2-inch, ML 3-inch and SB 4.2-inch mortars
  • Bishop, Chris. The Encyclopedia of Weapons of WWII.
  • Fendick, Rex F. Diary of a CANLOAN Officer (with the Middlesex Regt in NW Europe 1944-5) (self-published ed.). Saint John, NB.
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