Editing Tank destroyer (section)

=== United Kingdom ===
[[File:Achilles tank destroyer on the east bank of the Rhine.jpg|thumb|A British Achilles self-propelled anti-tank gun on the east bank of the [[Rhine]] following [[Operation Plunder]]]]
British tanks in the early years of the war, both [[infantry tank]]s and [[cruiser tank]]s, were (with the exception of the pre-war [[Matilda I (tank)|Matilda I]] design) equipped with a gun capable of use against contemporary enemy tanks—the 40&nbsp;mm [[Ordnance QF 2 pounder]]. This was replaced with the 57 mm [[Ordnance QF 6 pounder]] when that became available. There was extra impetus given to the development of anti-tank weaponry, which culminated in the 76mm [[Ordnance QF 17 pounder]], widely considered one of the best anti-tank guns of the war.<ref name="tanks4">Forty and Livesey 2006 p. 116</ref>

Towed anti-tank guns were the domain of the [[Royal Artillery]] and vehicles adapted to mount artillery, including anti-tank self-propelled guns such as the [[Deacon (artillery)|Deacon]] (6pdr on an armoured wheeled truck chassis) and [[Archer (tank destroyer)|Archer]] (17pdr on tracked chassis) and US-supplied vehicles, were their preserve rather than the [[Royal Armoured Corps]].

The self-propelled guns that were built in the "tank destroyer" mould came about through the desire to field the QF 17 pounder anti-tank gun and simultaneous lack of suitable standard tanks to carry it. As a result, they were of a somewhat extemporized nature. Mounting the gun on the [[Valentine tank]] chassis in a fixed superstructure gave the [[Archer (tank destroyer)|Archer]], looking somewhat like the light-chassis German [[Marder III]] in appearance. The 17 pounder was also used to re-equip the US-supplied [[M10 tank destroyer]], replacing the American 3-inch gun to produce the [[17pdr SP Achilles]].

In 1942 the General Staff agreed on investigating self-propelled mountings of the 6-pounder, 17-pounder, [[QF 3-inch 20 cwt|3-inch 20cwt]] guns and the 25-pounder field gun/howitzer on the [[Matilda II]], [[Valentine tank|Valentine]], [[Crusader tank|Crusader]] and [[Cavalier tank|Cavalier (Cruiser Mark VII)]] tank chassis. In October 1942 it was decided to progress using the Valentine chassis with a 17-pdr (which would become Archer) and 25-pdr (which entered service as [[Bishop (artillery)|Bishop]]).<ref>{{cite web| url = http://www.tankmuseum.org/museum-online/vehicles/object-e1969-43| title = S-P 17pdr, Archer (E1969.43)}}</ref>

While there was a general move to a general purpose gun that was usable against both tanks and in supporting infantry, there was a need to put the 17 pdr into a tank for use against the enemy's heavy tanks. The [[Cruiser Mk VIII Challenger]] was a project to bring a 17 pdr tank into use to support the [[Cromwell tank|Cromwell cruiser tank]]. Delays led to it being outnumbered in use by the [[Sherman Firefly]]—but a derivative of Challenger was the more or less open-topped variant ''Avenger'', which was delayed until post war before entering service. A cut-down 17 pdr, the 77mmHV was used to equip the [[Comet tank]] in the last year of the war.
[[File:Archer SP 17 pdr Tank Destroyer.jpg|thumb|Self-propelled 17pdr, Valentine, Mk I, Archer. The gun faced to the rear.]]

The closest the British came to developing an armoured tank destroyer in the vein of the German Jagdpanzers or Soviet ISU series was the Churchill 3-inch gun carrier—a [[Churchill tank]] chassis with a boxy superstructure in place of the turret and mounting a [[QF 3-inch 20 cwt|3-inch anti-aircraft gun]]. Although a number were ordered and fifty delivered in 1942,<ref>Chamberlain & Ellis, 1969. p68-69</ref> they were not put into service as the immediate threat passed. The design was rejected in favor of developing a 17 pounder armed Cromwell tank variant, ultimately leading to the [[Comet tank]]. The [[Tortoise (tank)|Tortoise]] "heavy assault tank", intended for use in breaking through fixed defensive lines, was well armoured and had a very powerful 32-pounder (94&nbsp;mm) gun, but did not reach service use.

By 1944, a number of the [[Sherman tank|Shermans]] in British use were being converted to [[Sherman Fireflies]] by adding the QF 17 pounder gun. Initially this gave each [[troop]] (platoon) of Shermans one powerfully armed tank. By war's end—through the production of more Fireflies and the replacement of Shermans by British tanks—about 50% of Shermans in British service were Fireflies. The Sherman Firefly, however, is not considered a tank destroyer since it could still perform the other duties of the regular [[M4 Sherman]], albeit the Firefly was less capable due to the late development of a HE round for the QF 17 pounder.