Stokes Mortar

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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
Type	Light mortar
Place of origin	United Kingdom
Service history
Used by	British Army, British Commonwealth armies United States
Wars	World War I
Production history
Designer	Sir Wilfred Stokes KBE
Designed	1915
Specifications
Weight	104 lbs total ^[1]
Crew	2

Shell	HE 10 lb 11 oz^[2]
Calibre	3 inch
Action	Trip
Elevation	45°-75° ^[5]
Rate of fire	25 rpm (maximum);^[3] 6-8 rpm (sustained)
Effective range	750 yards
Maximum range	800 yards^[4]
Filling	amatol
Filling weight	2lb 4 oz ^[6]

The 3 inch Stokes Mortar was a British trench mortar invented by Sir Wilfred Stokes KBE which was issued to the British Army and the Commonwealth armies during the latter half of the First World War.

1 History
2 Combat use
3 Range tables
4 Photo Gallery
5 See also
6 Surviving examples
7 Notes
8 References
9 External links

[edit] History

Frederick Wilfred Scott Stokes - later to become Sir Wilfred Stokes KBE - designed the mortar in January 1915. The British Army was at the time trying to develop a weapon which would be a match for the Imperial German Army's Minenwerfer mortar which was in use on the Western Front.

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.

Stokes' 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.

A modified version of the mortar firing a modern fin-stabilised streamlined projectile with a booster charge for longer range was developed after World War I ^[7] but was in effect a new weapon.

The Stokes Mortar remained in service until 1936, when it was superseded by the Ordnance ML 3 inch mortar, and some remained in use by New Zealand forces until after the Second World War.

As well as receiving a knighthood for inventing the mortar, Stokes was given several forms of monetary reward by the Ministry of Munitions for his invention including a royalty of £1 per Stokes mortar shell produced.

[edit] Combat use

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 detonate, firing the bomb towards the target.

The cast iron mortar bombs were 3 inches in diameter and were 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 4 additional "rings" of propellant were used for incrementally greater ranges. See range tables below. The 4 rings were supplied with the cartridge and gunners discarded the rings which were not needed.

The Stokes Mortar could fire as many as 25 bombs per minute and had a maximum range of 800 yards in World War I firing the original cylindrical unstabilised projectile.

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".^[8]

British Empire units had 1,636 Stokes mortars in service on the Western Front at the Armistice.^[9]

A 4 inch version was used to fire smoke and Thermit (incendiary) rounds but this should be considered a separate weapon to the standard 3 inch version firing high explosive rounds described in this article.

[edit] Range tables

(Provisional) Range Table For 3-Inch Stokes Mortar, Printed in September 1917.^[10]
Cartridge : 95 grains ballistite, reinforced with Charges : 5 grains, guncotton yarn
Rings : 110 grains, .3 mm flake cordite
Projectile : Bomb, 10 lb. 11 oz

	Cartridge Only		1 Ring		2 Rings		3 Rings		4 Rings
	Range	Time of Flight	Range	Time of Flight	Range	Time of Flight	Range	Time of Flight	Range	Time of Flight
degs	yds	secs	yds	secs	yds	secs	yds	secs	yds	secs
45	240	7·1	420	9·6	550	11·6	660	13·2	800	15·0
50	233	7·6	411	10·4	538	12·5	649	14·3	780	16·2
52	228	7·8	404	10·7	530	12·9	639	14·7	767	16·6
54	222	8·0	395	10·9	518	13·2	626	15·1	748	17·0
56	215	8·2	384	11·2	503	13·5	608	15·4	726	17·4
58	207	8·4	371	11·4	486	13·8	589	15·8	701	17·8
60	197	8·5	357	11·7	467	14·1	567	16·1	672	18·2
61	193	8·6	349	11·8	457	14·3	554	16·3	656	18·4
62	187	8·7	340	11·9	445	14·4	542	16·4	640	18·5
63	182	8·8	332	12·0	434	14·5	528	16·6	623	18·7
64	176	8·8	323	12·1	422	14·6	514	16·7	605	18·8
65	170	8·9	313	12·2	409	14·8	499	16·9	586	19·0
66	164	9·0	303	12·3	396	14·9	483	17·0	567	19·1
67	158	9·0	292	12·4	383	15·0	468	17·1	547	19·2
68	152	9·1	281	12·5	369	15·1	451	17·2	526	19·4
69	145	9·2	270	12·5	354	15·2	434	17·4	505	19·5
70	138	9·2	259	12·6	339	15·3	416	17·5	483	19·6
71	131	9·2	247	12·7	324	15·4	398	17·6	460	19·7
72	124	9·3	235	12·8	308	15·5	379	17·7	437	19·8
73	117	9·3	223	12·9	292	15·5	360	17·8	413	19·9
74	109	9·4	210	12·9	275	15·6	340	17·9	389	20·0
75	102	9·4	197	13·0	259	15·7	320	18·0	364	20·1

[edit] Photo Gallery

High Explosive bomb

Men of the KOYLI fusing Stokes shells near Wieltjie, October 1 1917

Troops adjusting fuzes on Stokes mortar bombs

Portuguese troops loading a Stokes mortar on the Western Front

[edit] See also

Wikimedia Commons has media related to:

3 inch Stokes Mortar

[edit] Surviving examples

Australian War Memorial, Canberra
An example with bombs is displayed at l'hotel de ville d'Arras, France.
Bernard Plumier : Link to his web page which has details and photograph Direct link to photograph

[edit] Notes

^ "Appendix D. Details of Trench Mortars" in "Field Artillery Notes No. 7". Mortar=48 lb; Elevating Stand=28 lb; Base Plate=28 lb; Total Weight for Transport = 104 lbs
^ "Appendix E. Details of Ammunition" in "Field Artillery Notes No. 7". This figure is for the unstabilised cylindrical bomb used in World War I.
^ "Appendix D. Details of Trench Mortars" in "Field Artillery Notes No. 7"
^ At 45° using 4 Rings of propellant. This figure is for the unstabilised cylindrical bomb used in World War I.
^ From Range Tables, September 1917. 45° gave maximum range with any particular propellant amount e.g. 420 yards with 1 ring. 75° gave the most vertical descent for the shell and the shortest range with any particular propellant amount e.g. 197 yards with 1 ring.
^ "Appendix E. Details of Ammunition" in "Field Artillery Notes No. 7"
^ Ruffell
^ Stokes's Trench Howitzer 3" Mark I, page 15
^ Farndale 1986, page 342
^ Range Tables transcribed and supplied courtesy of John Reed