Two-inch mortar

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Ordnance SBML two-inch mortar
2 inch mortar (AWM 094355).jpg
Australian infantrymen using a 2-inch (51 mm) mortar in New Guinea in 1945 (AWM 094355)
TypeLight mortar
Place of originUnited Kingdom
Service history
Used byBritish Commonwealth armies
other users
WarsWorld War II
Korean War[1]
Sino-Indian War[2]
Biafran War
Production history
VariantsMark 8 "airborne"
Mass10 12 pounds (4.8 kg)
Length21 inches (53 cm)

ShellHigh Explosive: 2 lb 2 oz (960 g).
Smoke: 2 pounds (910 g)
Illuminating: 1 lb 5 oz (600 g)
Calibre2 inch (50.8 mm)
Rate of fire8 rounds per minute
Effective firing range500 yards (460 m)

The ordnance SBML two-inch mortar, or more commonly, the "two-inch mortar", was a British mortar issued to the British Army and the Commonwealth armies, that saw use during the Second World War and later.

It was more portable than larger mortars, and the two-inch (51mm) had greater range and firepower than rifle grenades.


Although the British Army did use a 2-inch mortar during World War I, it was declared obsolete in 1919.[3][4] The two-inch mortar was developed during the 1930s from a Spanish 50mm mortar, manufactured by ECIA. Although refused for the British Army use as it stood, the Spanish mortar was modified by the Armament Research Department. In November 1937 ten examples of the new mortar were readied with 1,600 rounds each of high-explosive and smoke shells. The resulting trials confirmed the reliability and dependability of the weapon. The director of artillery ordered it to be placed in production in February 1938, only four months after the initial field trials, which meant that by 1939 some 500 of the weapons and their associated ammunition were already established in service as the Mk II, with crews trained in its use.[5]

Over the duration of the war the two-inch mortar was developed into eight separate marks, from which also stemmed a number of other variations. Some were successful and others less so; one of the latter, the "Weston" version, was developed in 1944, but was found to be less than satisfactory when used on soft ground. This weapon had the advantage of being fitted with an automatic recocking feature of the firing mechanism, but despite this it was withdrawn from use.[6]

The standard service version of the 2-inch (51 mm) mortar had a barrel length of 21 inches (530 mm) and could fire a high explosive bomb weighing 2.25 lb (1.02 kg) out to a range of 500 yards. With such a short barrel the normal firing method, where the bomb was dropped down the tube and a pin in the base of the barrel struck the detonator in the tail of the bomb, would not work so firing was by a small trigger mechanism at the breech. Originally the two-inch mortar was fitted with a large collimating sight with elevating and cross-level bubbles, but this was soon dropped as unnecessary for front-line use. It was replaced with a simple white line painted up the length of the barrel. The firer only had to line this up in the direction of the target and fire a number of bombs for effect. While this method of operation appeared rather haphazard, it worked well and the practice continued long after the war. The mortar evolved in other directions too, with the original large base plate being replaced by a simple curved model, to give it a combat weight of 10.25 lb (4.65 kg). Due to its small size, and for simplicity, the mortar had no forward strut or bipod that most larger designs needed. The barrel was held at the correct angle by one soldier while the other loaded and fired the round. It could achieve a firing rate of some eight rounds per minute. The bombs were cylindrical with a perforated four-finned tail. For the HE projectiles an impact fuze was fitted in the nose of the bomb. The illuminating round weighed 1 lb (0.45 kg) and the smoke round weighed 2.25 lb (1.02 kg). A whole range of other ammunition was also developed, including a specialised bomb that cast a lightweight explosive-filled net over minefields which could be detonated, clearing a path.[6]

Variants of the weapon itself included the Mk VII* with a shortened barrel, for use by airborne units, the Mk VII for use in Universal Carriers and the Mk III used as a smoke discharger in tanks.[6]

Post war, the two-inch mortar was kept in service to fire smoke and illuminating rounds. It remained in service until the late 1980s when it was replaced by the L9A1 51 mm light mortar.[6]


  • Calibre: 2 inches (50.8 mm)
  • Length: 21 inches (53 cm)
  • Weight: 10 12 pounds (4.8 kg)
  • Firing mechanism: Trip (small trigger)
  • Elevation: 45-90°
  • Range: 500 yards (460 m)
  • Rate of fire: Eight rounds per minute
Free Belgian Forces fire a two-inch mortar during a training exercise in Wales, 1941


  • Mk I = squad-level mortar introduced in 1918 and declared obsolete in 1919.[4]
  • Mk II = the first model introduced in 1938 with a large baseplate.[4]
  • Mk II* = the 1938 version intended for use with the Universal Carrier[4]
  • Mk II** = a second version for use with the Universal Carrier[4]
  • Mk II*** = version for use by infantry at platoon level and fitted with a large baseplate[4]
  • Mk III = version used as a smoke launcher for tanks[4]
  • Mk IV = limited production run and did not enter service[4]
  • Mk V = not manufactured[4]
  • Mk VI = not manufactured[4]
  • Mk VII = for use on Universal Carriers[4]
  • Mk VII* = for use by airborne forces, having a shorter barrel (14 inches (360 mm) = 36 cm) and a baseplate replaced with a spade-like plate[4]
  • Mk VII** = infantry use with long barrel and spade-like baseplate[4]
  • Mk VIIA = Indian Army model[7]
  • Mk VIII = another short-barrelled version for the airborne forces[7]

Ammunition type (plus round weight and colour)[edit]

  • High explosive (HE): 2.25 lb (1.02 kg) - olive drab body, red band[4]
  • White phosphorus smoke (WP Smk): 2.25 lb (1.02 kg) - dark green body[4]
  • Titanium tetrachloride smoke (FM Smk): 2 lb (0.91 kg) - dark green body[4]
  • Illumination (Ill): 1 lb (0.45 kg) - drab khaki (light OD) body[4]
  • Signal multi star (Sig): 1 lb (white 2 lb) - light stone (grey) body. NB: the multi-star was available in white, red, green, and mixed red/green.[4]

Ammunition was packed 1 x 51mm-shell per tube, 3 conjoined tubes per pack (3 shells), 2 packs (6 shells) to a fibre container, and three fibre containers to a steel box (18 shells total).[8]

Modern variants[edit]

India’s Ordnance Factory Board's 51mm E1 mortar is an enhanced version of the two-inch British mortar of World War II; it is still in production and service in India.[9]


  • Calibre: 51.25mm (2 in)
  • Weight: 4.88 kg
  • Range: 200-850m
  • Rate of fire:
    • normal: eight rounds per minute
    • high: 12 rounds per minute
  • Bomb weight:
    • High explosive: 950g (800m range)[10]


See also[edit]

Similar, World War 2-era weapons


  1. ^ a b "Mortar - 2 inch" (PDF). Defence unexploded ordnance website: ordnance information sheet. March 2015.
  2. ^ Mohan Guruswamy (November 20, 2012). "Don't forget the heroes of Rezang La". The Hindu. Retrieved 28 March 2015.
  3. ^ Bishop 1998, p. 193.
  4. ^ a b c d e f g h i j k l m n o p q r Norris 2002, p. 12.
  5. ^ a b Norris 2002, p. 10.
  6. ^ a b c d Norris 2002, p. 11.
  7. ^ a b Norris 2002, p. 13.
  8. ^ Owen, J.I.H. (editor); Brassey's Infantry Weapons of the World (1950-1975), pg. 134, Bonanza Books, New York. (1978)
  9. ^ Kemp, Ian (October 2017). "Light mortars, heavy effect" (PDF). Asian Militairy Review: 21–30. Archived from the original (PDF) on 2 March 2012.
  10. ^ "Mortars & Ammunitions". May 2009. Archived from the original on 27 October 2014.
  11. ^ a b Rottman, Gordon L. (20 Nov 2015). Victory 1945: Western Allied Troops in Northwest Europe. Elite 209. Osprey Publishing. p. 60. ISBN 9781472809476.
  12. ^ Gates & Roy 2014, p. 48.
  13. ^ Gates & Roy 2014, p. 77.
  14. ^ Young, Peter (1972). The Arab Legion. Men-at-Arms. Osprey Publishing. p. 24. ISBN 978-0-85045-084-2.
  15. ^ Gates & Roy 2014, p. 70.
  16. ^ Stack, Wayne; O’Sullivan, Barry (20 Mar 2013). The New Zealand Expeditionary Force in World War II. Men-at-Arms 486. Osprey Publishing. p. 19. ISBN 9781780961118.
  17. ^ Jowett, Philip (2016). Modern African Wars (5): The Nigerian-Biafran War 1967-70. Oxford: Osprey Publishing Press. p. 23. ISBN 978-1472816092.
  18. ^ Norris 2002, p. 5.