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Old January 14th, 2022, 03:50 AM

Charles M Charles M is offline
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Default 18 and 25 pdr AP capability

At first I wanted to query the absence of any AP capability for these guns, but a closer look of the game specs revealed other issues.

The "18 pounder field gun" is a mystery. Firstly, the icon suggests the gun is the 18 pounder of Great War vintage with large narrow wooden wheels. However, the photo used shows an 18/25 pdr as used in France 1940. As shown this had wider but smaller wheels with pneumatic tyres for vehicle towing. So what is it meant to be? The old 18 pdr was still in use in world war two, but only in Britain, on the Sudan-Eritrean border and during the early stages of the Burma campaign. The old 18 pdr carriages, both the split-trail, and the humped box trail, were used with the new 25 pdr barrel inserted to form the 18/25 pdr, also known officially as the 'Ordnance QF 25 pdr Mark I'. These were sent to France in April 1940 whereas the Mark II version, the 25 pdr proper, was first used in Norway that spring.

In WinSPWW2 the AP outfit for the British 18 pdr (Unit Nos. 127 and 137) 25-pdr field guns (Unit Nos. 065, 119 and 152) need correcting as both these guns were issued with AP ammunition for self-defence. The fact that these guns were used against tanks in France appears to have been overlooked, or discounted. Although Unit No. 680 covers the 25 pdr in the AT role, it is not available before 1941 (for North Africa), this is incorrect.

Initially the General Staff, when in 1938 they decided that anti tank defence in the British army should pass from the infantry to the artillery, determined that field guns fighting enemy tanks, should be issued with 'plugged HE'. This was an HE round from which the percussion fuse was removed. Plans were made to also fit a metal cap which, it was hoped, would help to penetrate armour plate. After much delay, common sense eventually prevailed and a solid steel shot was produced in 1939 for the 18 pdr, for the 18/25 pdr and for the 25 pdr proper.

I have no figures for 18 pdr AP shot performance but it would have been similar to that quoted for the 25 pdr, which is quoted by Hogg as 70mm vertical armour at 400 yards, as the 18 pound projectile used the same charge as the standard 18 pound HE shell, giving the latter 1625 feet per second, whereas the early 18/25 pdr and 25 pdr had charges for 1550 feet per second to propel a 20 pound projectile. Bird and Livingston, p. 60 in their detailed study give the following estimated penetration figures for the 25 pdr: with an mv of 1550 fps, at 500 yards 66mm at 90 degrees impact against homogeneous armour, and 74 mm against face-hardened, and at 1897 fps, 86mm and 95mm respectively. These rounds were more than enough to see off German tanks in 1940. The later 25 pdr, given additional charges and fitted with a muzzle brake, managed 2000 fps with corresponding increases in armour penetration.

Perhaps the data for the 18 pdr troop, No. 137, the 25 pdr Unit Nos. 065, 119 and 152 can be changed. In the game the 25 pdr Howitzer, No. 152, gets 3 "sabot [sic]" rounds. The LCG (M) (I) Unit No. 102 gets 24 rounds. I presume that this is meant to be AP shot. There was nothing special about this ammunition – it was unsophisticated steel shot. I do not know if the 3 or 24 rounds allocated represents 3 and, respectively, 24 shots but it is suspect. Why Unit No. 680 gets 40 x “sabot” is perplexing, as – again - ordinary steel AP shot was supplied.

The Bishop SP (Unit No. 45 in Win SPWW2) had 11 AP rounds whereas in the game it has no AP capability, and the Sexton (Unit No. 047 in WinSPWW2) had 18, whereas in the game it has no AP but 7 "sabot [sic]" rounds. The towed 25-pdr only had 8 such AP rounds, later increased to 12. I suspect the issue for the 18 pdr was identical. Given the low velocity of the gun, AT defence was very much a close-range business. No HEAT round was ever issued for these guns, although work to develop such a round continued unsuccessfully until dropped in 1944. The plugged HE metal cap should not be confused with a soft metal piercing cap fitted later to AP rounds to defeat German face-hardened armour, and the 25-pdr never had such APCBC or similar ammunition since it was realised that the low velocity of the weapon would not enhance performance and thus made the issue of such new ammunition types pointless.

Sources:

Lorrin Rexford Bird & Robert D. Livingston, World War Two Ballistics: Armor and Gunnery, Overmatch Press, New York, 2nd edition, 2001

Various correspondence with Colonel P.R.R. De Burgh, OBE, Royal School of Artillery, Larkhill, England including:

25-pounder AP shot range tables dated 11 October 1939 and copy of:

Brigadier A.L. Pemberton, M.C, The Development of Artillery Tactics and Equipment, War Office, 1950

D.P. Dyer, Carrier Valentine 25-pdr Gun Mk I, Belona Military Vehicle Print # 31, Hemel Hempstead, 1972

Terry Gander, 'Sexton', Military Modelling, March 1982

Chris Henry, The 25-pounder Field Gun 1939-1972, New Vanguard #48, Osprey Publishing, Botley, 2002

Ian V. Hogg, British and American Artillery of World War Two, Arms & Armouir Press, London 1978

B.T. White, British Tanks and Fighting Vehicles 1914-1945, Ian Allen, London, 1970
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Old January 14th, 2022, 05:12 AM
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Mobhack Mobhack is online now
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Default Re: 18 and 25 pdr AP capability

Sabot is used in field guns for a reduced-range AP round since the basic round has a huge range. The game does a steadt pull-down based on gunrange for AP so the long ranges of the HE round are not a good basis for an AP round. Sabot is also used for weak AP like in the short french 37mm Puteax gun. The sabot-AP round has a shorter range so the AP value will fall off quicker.

Read the Mobhack help if you need details on game mechanics.
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