The Sherman Firefly was a medium tank used by the United Kingdom and some armoured formations of other Allies in the Second World War.

Conceived as a stopgap until future British tank designs came into service, the Sherman Firefly became the most common vehicle mounting the 17-pounder in the war.

After the problem of getting such a large gun to fit in the Sherman's turret was solved, the Firefly was put into production in early 1944, in time to equip the 21st Army Group, commanded by General Bernard Montgomery, for the Normandy landings.

[5][page needed] Major George Brighty of the Royal Tank Regiment was at the Lulworth Armoured Fighting School in early 1943.

[5] Around June 1943, a colleague of Brighty, Lieutenant Colonel George Witheridge of the Royal Tank Regiment, arrived at Lulworth.

During the Battle of Gazala in mid-1942, Witheridge had been blown out of his M3 Grant medium tank and though he recovered from his wounds, he was declared unfit to return to combat duty.

Unwilling to abandon the project, Witheridge, using his connections with such influential people as Major General Raymond Briggs, former General Officer Commanding the 1st Armoured Division in North Africa and then director of the Royal Armoured Corps, successfully lobbied Claude Gibb, Director-General of Weapons and Instruments Production at the Ministry of Supply, to make it an official ministry project.

He had liaised with Colonel William Watson, who in late 1942 had returned from secondment to Australia to work on the production of the Australian AC1 Sentinel tank, onto which the 17-pounder had been mounted.

[4][7] W. G. K. Kilbourn, a Vickers engineer working for the DTD, transformed their idea into the reality of the prototype of the tank that would serve the British forces from the invasion of Normandy in June 1944.

The Firefly had no armour or mobility advantages over the normal Sherman tank beyond the additional 13 mm of protection added to its mantlet.

The 17-pounder's larger breech and recoil system made it significantly more difficult for the loader to exit quickly; a new hatch was cut into the top of the turret over the gunner's position to resolve this.

This left the Firefly as the only tank available with firepower superior to the QF 75 mm gun in the British arsenal, earning it the "highest priority" from Winston Churchill.

[note 2] The name "Firefly" in period sources often refers to any vehicle with a 17-pounder gun, often the 17pdr SP Achilles M10C variant of the M10 tank destroyer.

[13] Though the 17-pounder had superior anti-tank capabilities, it lacked an effective HE round and was thus inferior to the standard Sherman 75 mm gun against soft targets, such as infantry, buildings and lightly armoured vehicles.

The cramped turret meant that loading the large shell was difficult, so the Firefly had a slower rate of fire than a standard M4 Sherman.

[9] Since the Firefly was a stopgap, these problems were never eliminated, as it was supposed to be retired with the introduction of the new British tank designs such as the Comet and later Centurion.

A .50-inch (12.7 mm) M2 Browning heavy machine gun was also fitted on the turret roof, though many crews removed it, due to its awkward mounting and position near the commander, which limited a full 360-degree view when the hatch was open.

[citation needed] To complicate matters, a very small number of Canadian license-built Sherman IIs (M4A1), the Grizzly, were converted to Fireflies in Canada and used for training, but none saw action.

[16] In late 1944, with the creation of an effective high-explosive shell for the 17-pounder gun, British units started to receive two Fireflies per troop.

[9] Production of the Sherman Firefly reached some 2,100 – 2,200 tanks; exact numbers are hard to determine as documents give contradictory totals.

The timing was fortunate as Allied intelligence had begun to realize in early 1944 through statistical analysis that the Germans were fielding a much larger number of more formidable tanks (such as the Panther) than had been anticipated.

This information was slow to reach Allied military planners, who had mistakenly assumed the Panther, like the Tiger, would be a rare heavy tank with a limited production run, so the number of Panthers deployed came as a surprise to Allied formation commanders and tank crews forced to engage them with guns that could not penetrate the frontal armor except at short range.

When moving, the gun's overlap in front or, if traversed, to the side is so long that the driver, gunner, and commander have to be constantly alert to avoid wrapping the barrel around some apparently distant tree, defenseless lamp-post or inoffensive house.

[9] Despite being a high-priority target, Fireflies appear to have had a statistically lower chance of being knocked out than standard Shermans, probably due more to how they were employed than to the effectiveness of the camouflaging of the long barrel.

[4] Given the high value placed on Fireflies, a common tactic was for commanders to reconnoitre the battlefield before a battle, to look for good overwatch positions.

Harris of the 4th/7th Dragoon Guards, along with three standard Shermans, set up defensive positions along with the infantry after capturing the village of Lingèvres, near Tilly-sur-Seulles, France.

[24][25][26] From this position, they overlooked a large open section of ground and were able to watch as German tanks advanced up Route Nationale 158 from the village of Cintheaux.

Joe Ekins, the gunner of Sergeant Gordon's Sherman Firefly (Velikye Luki – A Squadron's tanks were named after towns in the Soviet Union) had yet to fire his gun in action.

[citation needed] In 1947, the Argentine Army purchased surplus armament that was stored in Belgium, including some 200 Sherman Fireflies of all sub-types; they were in use from 1948.

Starting in 1959, 150 Fireflies Mk.V had their original Chrysler A57 engine substituted for a Ford GAA V8, to improve reliability; these remained in service until the mid-1970s.