2-inch mortar

Infobox Weapon
name=Ordnance SBML 2-inch mortar


caption=Australian infantrymen using a 2-inch mortar in New Guinea in 1945 (AWM 094355)
origin=flagcountry|United Kingdom
type=Light mortar
is_UK=yes
is_ranged=yes
is_bladed=
is_explosive=yes
is_artillery=yes
is_vehicle=
service=
used_by=British Commonwealth armies
wars=World War II, Korean War
designer=
design_date=
manufacturer=
production_date=
number=
variants= Mark 8 "Airborne"
weight=10½ lb (4.8 kg)
length=21 inches (53 cm)
part_length=
crew=Two
cartridge="HE (high explosive)":
2 lb 2 oz (1 kg).
"SMK (smoke)":
2 lb (909 g)
"ILL (illuminating)":
1 lb 5 oz. (596 g)
caliber=2 inch
action=Trip
rate=8 rounds per minute
velocity=
range=500 yards (457 m)
max_range=
feed=
sights=
breech=
recoil=
carriage=
elevation=45-90°
traverse=
diameter=
filling=
filling_weight=
detonation=
yield=The Ordnance SBML 2-inch mortar, or more commonly just "2-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 had the advantages of being more portable than larger mortars which needed vehicles to be carried around, but gave greater range and firepower than rifle grenades.

History

The British Army had two types of mortar in service at the outbreak of the Second World War, one of which was the 2-inch weapon for use with infantry platoons. The 2-inch mortar had been developed during the 1930s after the British Army had inspected weapons of a similar calibre in service with other European countries, including the Spanish 50mm mortar. Although deemed unsuitable for the British Army as it stood, the Spanish mortar did serve as the starting point from which the Armament Research Department could begin development of its own version. In November 1937 ten examples of the new weapon were readied with 1600 rounds each of high-explosive and smoke bombs. The resulting trials confirmed the reliability and dependability of the weapon. The Director of Artillery ordered the weapon 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 the use of the weapon.

Over the duration of the war the 2-inch mortar was developed into no fewer than eight separate marks, from which also stemmed a number of other variations. Some were successful and others less so, such as the Weston version developed in 1944 and found to be less than satisfactory when used on soft ground. This version had the advantage of being fitted with an automatic recocking feature of the firing mechanism, but despite this it was withdrawn from use.

The standard service version of the 2-inch mortar had a barrel length of 21 inches and could fire a high explosive bomb weighing 2.25lb 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 2-inch mortar was fitted with a large collimating sight with elevating and cross-level bubbles, but this was soon dropped as unnecessary in a front-line unit. It was replaced instead 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. Whilst this method of operation may sound 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 10.25lb. Due to its small size, and for simplicity the mortar had no forward strut or bipod like larger designs needed. The barrel would be 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 projectile an impact fuze was fitted in the nose of the bomb. The illuminating round weighed 1lb and the smoke round weighed 2.25lb. A whole range of other ammunition was also developed including a specialised bomb that cast a lightweight explosive-filled net over patches in minefields so that it could be detonated to clear a path.

Versions of the weapon itself included the Mk VII* with a shortened barrel, for use by airborne units, the Mk VII for use in Universal (Bren Gun) Carriers and the Mk III used as a smoke discharger in tanks.

Post war, the 2-inch mortar was kept in service to fire smoke and illuminating rounds. The mortar remained in service until the late 1970s when it was replaced by the Royal Ordnance 51 mm infantry mortar.

pecifications

*Caliber: 2 inches (50.8 mm)
*Length: 21 inches (53 cm)
*Weight: 10½ lbs (4.8 kg)
*Firing mechanism: Trip (small trigger)
*Elevation: 45-90°
*Range: 500 yards (457 m)
*Rate of fire: 8 rounds per minute

Variations

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

Ammunition type (+ round weight and colour)

*High explosive (HE): 2.25lb - olive drab body, red band
*White phosphorus smoke (WP SMK): 2.25 lb - dark green body
*Titanium tetrachloride smoke (FM SMK): 2lb - dark green body
*Illumination (ILL): 1lb - drab khaki (light OD) body
*Signal Multi Star: 1lb (white 2lb) - light stone (grey) body

note: the Multi Star available in white, red, green, and red/green mixed

ee also