|3 inch Stokes mortar|
Sir Wilfred Stokes with example of his mortar and bombs. Typical 3-inch bombs used are 2nd and 6th from left
|Place of origin||United Kingdom|
|Designer||Sir Wilfred Stokes KBE|
|Mass||104 lbs (47.17 kg) total|
|Shell||HE 10 lb 11 oz|
|Calibre||3.2 in (81 mm)|
|Rate of fire||25 rpm (maximum)|
6-8 rpm (sustained)
|Effective firing range||750 yards (686 m)|
|Maximum firing range||800 yards (731 m)|
|Filling weight||2lb 4 oz (1 kg)|
The Stokes mortar was a British trench mortar designed by Sir Wilfred Stokes KBE that was issued to the British and U.S. armies, as well as the Portuguese Expeditionary Corps, during the later half of the First World War. The 3-inch trench mortar is a smooth-bore, muzzle-loading weapon for high angles of fire. Although it is called a 3-inch mortar, its bore is actually 3.2 inches or 81 mm.
Frederick Wilfred Scott Stokes - who later became Sir Wilfred Stokes KBE - designed the mortar in January 1915. The British Army was at the time trying to develop a weapon that would be a match for the Imperial German Army's Minenwerfer mortar, which was in use on the Western Front.
Stokes's design was initially rejected in June 1915 because it was unable to use existing stocks of British mortar ammunition, and it took the intervention of David Lloyd George (at that time Minister of Munitions) and Lieutenant-Colonel J. C. Matheson of the Trench Warfare Supply Department (who reported to Lloyd George) to expedite manufacture of the Stokes mortar.
The Stokes mortar was a simple weapon, consisting of a smoothbore metal tube fixed to a base plate (to absorb recoil) with a lightweight bipod mount. When a mortar bomb was dropped into the tube, an impact sensitive primer in the base of the bomb would make contact with a firing pin at the base of the tube, and ignite the propellant charge in the base, launching the bomb towards the target. The warhead itself was detonated by an impact fuse on reaching the target.
The barrel is a seamless drawn-steel tube necked down at the breech or base end. To the breech end is fitted a base cap, within which is secured a firing pin protruding into the barrel. The caps at each end of the bomb cylinder were 81 mm diameter. The bomb was fitted with a modified hand grenade fuze on the front, with a perforated tube containing a propellant charge and an impact-sensitive cap at the rear.
Range was determined by the amount of propellant charge used and the angle of the barrel. A basic propellant cartridge was used for all firing, and covered short ranges. Up to four additional "rings" of propellant were used for incrementally greater ranges. The four rings were supplied with the cartridge and gunners discarded the rings that were not needed.
One potential problem was the recoil, which was "exceptionally severe, because the barrel is only about 3 times the weight of the projectile, instead of about one hundred times the weight as in artillery. Unless the legs are properly set up they are liable to injury".
A modified version of the mortar, which fired a modern fin-stabilised streamlined projectile and had a booster charge for longer range, was developed after World War I; this was in effect a new weapon.
The mortar was in no sense a new weapon, although it had fallen out of general usage since the Napoleonic era. In fact, while the British and French worked on developing new mortars, they resorted to issuing century-old mortars for use in action.
The Stokes mortar remained in service into the Second World War, when it was superseded by the Ordnance ML 3 inch mortar, and some remained in use by New Zealand forces until after the Second World War.
The French developed an improved version of the Stokes mortar as the Brandt Mle 27, further refined as the Brandt Mle 31; this design was widely copied with and without license. Despite their indigenous production, out of 8,000 81 mm mortars in service with the French in 1939, 2,000 were of the original Mk. I build purchased from Great Britain.
In World War I, the Stokes mortar could fire as many as 25 bombs per minute and had a maximum range of 800 yards firing the original cylindrical un-stabilised projectile. British Empire units had 1,636 Stokes mortars in service on the Western Front at the Armistice. By World War II, it could fire as many as 30 bombs per minute and had a range of over 2,500 yd (2,300 m) with some shell types. A 4 in (100 mm) version was used to fire smoke, poison gas and thermite (incendiary) rounds but this should be considered a separate weapon to the standard 3 in (76 mm) version firing high explosive rounds described in this article. The Stokes mortar was used in the Banana Wars and helped American forces defeat Sandinista rebels during the Second Battle of Las Cruces on 1 January 1928. The Paraguayan Army made extensive use of the Stokes mortar during the Chaco War, especially as a siege weapon in the Battle of Boquerón in September 1932. Stokes mortars were widely used by the Republican Army during the Spanish Civil War. In September 1936, 44,000 Stokes rounds arrived to Spain.
About 700 Stokes mortars were acquired by Poland between 1923 and 1926.