The Sherman Firefly was a medium tank used by the United Kingdom and some armoured formations of other Allies in the Second World War. It was based on the US M4 Sherman but was fitted with the more powerful British calibre 17-pounder anti-tank gun as its primary weapon. 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.
The British Army made extensive use of Sherman tanks, but they expected to have their own tank models developed soon, so the idea of mounting the 17-pounder in the Sherman was initially rejected. However, through the efforts of two persistent British officers, government reluctance was eventually overcome, and the Firefly went into production. This proved fortunate, as the Cruiser Mk VIII Challenger and Cruiser Mk VIII Cromwell tank designs experienced difficulties and delays.
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. It soon became highly valued, as its gun could almost always penetrate the armour of the Panther and Tiger tanks it faced in Normandy, something no other British or American tank could reliably do.Milner, Marc, (2014) Stopping the Panzers, University of Kansas Press, 1 Because the Firefly's barrel was visibly longer than that of a normal 75 mm Sherman, crews tried to countershade camouflage it so the tank would look like a regular Sherman from a distance. Between 2,100 and 2,200 were manufactured before production ended in 1945; it is unknown if this includes 100 tanks built for the United States.
Origins The idea of fitting a 17-pounder gun into a Sherman tank was rejected by the Ministry of Supply's Tank Decision Board. Although the British Army had made extensive use of the American-built Sherman, it was intended that a new generation of British tanks would replace it. First, there was the Cromwell, which was expected to use the Vickers high-velocity 75 mm gun; this gun would have had superior anti-tank performance to the US 75 mm and 76 mm guns that were mounted in the Sherman. The second was the A30 Challenger, which was based on the Cromwell but with the even more powerful 17-pounder gun.J. Buckley (2004) These two tanks and their successors—the Comet and the Centurion, which were already on the drawing board—were to replace the Sherman in British service and the prospect of diverting resources to mount the 17-pounder on the Sherman seemed undesirable.Fletcher (2008)
Major George Brighty of the Royal Tank Regiment was at the Lulworth Armoured Fighting School in early 1943. Despite the A30 Challenger undergoing initial trials at Lulworth, Brighty was convinced that the Sherman was a better mount for the 17-pounder. The turret of the Sherman was too small to allow for the very long recoil of the gun. In a radical adjustment, Brighty removed the recoil system and locked the gun in place, thus making the entire tank absorb the recoil, but this was far from an ideal situation, and there was no telling how long the tank would have been able to handle such a setup.
Around June 1943, a colleague of Brighty, Lieutenant Colonel George Witheridge of the Royal Tank Regiment, arrived at Lulworth. A veteran of the North Africa campaign, Witheridge had experienced first-hand the one-sided battles between British tanks armed with the 40 mm 2-pounder gun and Rommel's formidable tanks and anti-tank guns. 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. In January 1943, he was posted to Fort Knox in the United States for six months to advise on gunnery, where he was "sold" on the Sherman.Fletcher (2008), p. 10 While at Lulworth, Witheridge inspected the A30 Challenger and "joined in the chorus of complaints" about the tank. Upon looking up Brighty and learning of his attempts to improve the Sherman, Witheridge lent his assistance. He advised Brighty on methods to solve the recoil problem.
Not long after, Witheridge and Brighty received a notice from the Department of Tank Design (DTD) to cease their efforts. 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. Gibb was able to explain to the detractors that not only was it possible, but it should be doable in England. 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. With this development, the endeavor was taken out of the hands of the highly enthusiastic and devoted amateurs at Lulworth who had initiated it and given to professional tank developers.Fletcher (2008), pp. 11–12
Design
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 first thing he had to fix was the lack of a workable recoil system for the 17-pounder. The 17-pounder traveled back as it absorbed the recoil of the blast. This was too long for the Sherman's turret.Fletcher (2008), p. 13 Kilbourn solved this problem by redesigning the recoil system completely rather than modifying it. The recoil cylinders were shortened and placed on both sides of the gun to take advantage of the width of the turret.
The gun breech itself was also rotated 90 degrees to allow loading from the left rather than from on top.Hart (2007), US-designed tanks put the gunner on the right and loader on the left. British practice was the reverse. The radio, normally mounted in the back of the turret in British tanks, had to be moved; an armoured box (a "bustle") was attached to the back of the turret to house it, with access through a large hole cut through the turret.
The next problem encountered by Kilbourn was that the gun cradle, the metal block on which the gun sat, had to be shortened to allow the gun to fit into the Firefly, and thus the gun itself was not very stable. Kilbourn had a new barrel designed for the 17-pounder that had a longer untapered section at the base, which helped solve the stability problem. A new mantlet was designed to house this gun and the modified cradle. 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 modifications were extensive enough that 17-pounders intended for the Firefly had to be factory-built specifically for it.
Kilbourn had to deal with additional complications. On the standard Sherman tank, there was a single hatch in the turret through which the commander, gunner, and loader entered and exited the tank. 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.Fletcher (2008), p. 14 The final major change was the elimination of the hull gunner in favour of space for more 17-pounder ammunition, which was longer than the original 75 mm.
By October and November 1943, enthusiasm began to grow for the project. The 21st Army Group was informed of the new tank in October. Even before final testing had taken place in February 1944, an order for 2,100 Sherman tanks armed with the 17-pounder gun was placed, as the Challenger program was suffering constant delays and it was realized that few would be ready for Normandy. Even worse, it was discovered that the Cromwell did not have a turret ring wide enough to take the new High Velocity 75 mm gun (50 calibres long), so it would have to be armed with the general purpose Ordnance QF 75 mm. 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.
Name The nickname "Firefly" was a British nickname given to armored vehicles with an adapted 17-pounder due to either the bright muzzle flash or because of the detonation of leftover gunpowder while firing, creating a flash that was directed towards both the gunner and loader. The nickname was only recorded to be used by the British army and was never officially adopted. During the war, Shermans with 17-pounder guns were usually known as "1C", "1C Hybrid", or "VC", depending on the basic mark of the vehicle. In British nomenclature, a "C" at the end of the Roman numeral indicated a tank equipped with the 17-pounder.for more on the explanation of the various marks, see Lend-Lease Sherman tanks#British nomenclature
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.
Armament
The main armament of the Sherman Firefly was the Ordnance Quick-Firing 17-pounder. Designed as the successor to the British QF 6-pounder, the 17-pounder was the most powerful British tank gun of the war, and one of the most powerful of any nationality, being able to penetrate more armour than the 8.8 cm KwK 36 fitted to the German Tiger I. The 17-pounder was theoretically able to penetrate some of armour at and at using standard armour piercing, capped, ballistic capped (APCBC) ammunition. Armour piercing, discarding sabot (APDS) ammunition could penetrate some 256 mm of armor at 500 m and 233 mm at 1,000 m, which on paper could defeat the armour of almost every German armoured fighting vehicle at any likely range. However, war production APDS rounds lacked accuracy, and the 50 mm penetrator was less destructive after it had penetrated enemy tank armour than the 76.2 mm APCBC shell. APDS ammunition was rare until the post-war period. While the Sherman Firefly was capable of carrying 77 rounds of ammunition, the tank's design features meant that only 23 rounds were easily and readily available when the tank was in action.
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. As the war in Europe neared its close, the Allies found themselves encountering these more often than heavy German tanks. Allied tank units, therefore, typically refused to completely switch to Fireflies. A good HE shell for the gun only became available in late 1944 and even then was not as potent as the standard Sherman 75 mm HE shell.