The Ordnance SBML two-inch mortar, or more commonly, just "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 had greater range and firepower than
rifle grenades. Its main purpose was to produce smoke for cover and through high trajectory and HE shell, engage targets "immune to small arms fire".[3]
Design
The two-inch mortar was one of a number of small mortars brought into service by European nations between the two World Wars.
Due to its small size, and for simplicity, the mortar had no forward strut or bipod like larger designs needed. The barrel was held at the correct angle by one soldier while the other loaded and fired the round. The original design had a large base plate and sights for aiming which used
spirit levels. As the design matured, the baseplate became smaller and the sights were omitted; aiming was by eye and relied on the firer's judgment and experience. With such a short barrel, the typical 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.
The bombs were cylindrical with a (perforated) four finned tail. For the HE projectile an impact
fuze was fitted in the nose of the bomb.
Postwar, the two-inch mortar was kept in service to fire smoke and illuminating rounds. It was replaced by the
Royal Ordnance 51 mm infantry mortar[4] in the late 1980s.
Specifications
Calibre: 2 inches (50.8 mm)
Length: 21 inches (53 cm)
Weight: 10+1⁄2 pounds (4.8 kg)
Firing mechanism: Trip (small trigger)
Elevation: 45-90°
Range: 500 yards (460 m)
Rate of fire: Eight rounds per minute
Variants
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.[5]
Mk II - the first model introduced in 1938 with a large baseplate.[5]
Mk II** - a second version for use with the Universal Carrier[5]
Mk II*** - version for use by infantry at platoon level and fitted with a large baseplate[5]
Mk III - version used as a smoke bomb launcher for tanks[5] It was built into the turret and could fire smoke shells from 20 to 120 yd (18 to 110 m) away. The range was varied by using a gas regulator to adjust the escaping propellant gases. It was aimed and fired by using a pistol grip at the back that would activate the firing pin when the trigger was pulled.
Mk IV - limited production run and did not enter service[5]
Signal multi-star (Sig): 1 lb (0.45 kg) - white body and 2 lb (0.91 kg)) - grey body. The multi-star was available in white, red, green, and mixed red-green.[5]
Ammunition was packed one 51 mm-bomb per tube, three conjoined tubes per pack (three bombs), two packs (six bombs) to a
fibre container, and three fibre containers to a steel box (18 bombs total).[7]
Modern variants
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.[8]
United States The Mk.III (renamed the M3 mortar) was used by the US Army on the M4 Sherman from late 1943 to early of 1945. The vehicle's combat load was 18 smoke shells for M4 tanks with the 75 or 76 mm cannon to 12 shells for M4 assault tanks with the 105 mm howitzer.
^Stack, Wayne; O’Sullivan, Barry (2013). The New Zealand Expeditionary Force in World War II. Men-at-Arms 486. Osprey Publishing. p. 19.
ISBN9781780961118.
^Jowett, Philip (2016). Modern African Wars (5): The Nigerian-Biafran War 1967-70. Men-at-Arms. Oxford: Osprey Publishing Press. p. 23.
ISBN978-1472816092.