Sherman Firefly

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 an even more powerful 17-pounder gun.[3] 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.[4]

Several unofficial attempts were made to improve the firepower of the Sherman. The earliest can be credited to Major George Brighty of the Royal Tank Regiment while he 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 a far from ideal situation and there was no telling how long the tank would have been able to handle such a set-up.[4]

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 tanks.[5] 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.[3] 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 now 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.[3][6]

Rear view of the Firefly at the Bovington Tank Museum showing the external radio "bustle".

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 Kilbourn had to fix was the lack of a workable recoil system for the 17-pounder. The 17-pounder traveled 40 in (1.0 m) back as it absorbed the recoil of the blast. This was too long for the Sherman's turret.[7] 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.[8][note 1] 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 un-tapered 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.[4][8]

Kilbourn had to deal with other problems. On the standard Sherman tank, there was a single hatch in the turret through which the commander, gunner, and loader entered and left 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.[9] 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 1943. 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.[3]

The nickname "Firefly" was adopted due to the bright muzzle flash of the main gun.[10] It was sometimes used at unit level (brigade/regiment) in war diaries from March 1944, along with "Mayfly". 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.[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.

Loading 17-pounder APCBC rounds into a Firefly

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 163 mm (6.4 in) of armour at 500 m (550 yd) and 150 mm (5.9 in) at 1,000 m (1,100 yd) 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.[11] 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, design features of the tank meant only 23 rounds were easily and readily available when the tank was in action.[12]

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.[3]

Another problem was that the powerful blast from the 17-pounder gun kicked up large amounts of dirt as well as smoke, making it difficult for the gunner to observe the fall of the shot (and forcing him to rely on the commander to observe it and to order corrections) and revealing the position of the tank (forcing the Firefly to move every few shots). The recoil and muzzle blast could be severely jarring to Firefly crews and the muzzle blast frequently caused night blindness. The latter was a problem common to any tank armed with a high-velocity gun, including the Panther and Tiger I. 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.[8] 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.

British Army Sherman Tulip on the left. Note the 17-pounder gun, countershaded to appear like the standard 75 mm gun seen on the center tanks.

The Firefly's secondary armament was the standard 0.3 inch (7.62 mm) Browning M1919 machine gun coaxial in the turret, the hull-mounted machine gun being removed to increase ammunition storage for the main gun. 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.

In 1945, some British Fireflies were fitted with a rail on either side of the turret for two RP-3 "60lb" high-explosive 3-inch rockets. Called "Sherman Tulips", these were used at the Rhine Crossing by the 1st Bn Coldstream Guards. The rockets, accurate when fired from aircraft, were less accurate when fired from a stationary platform, such as a tank, as they had little initial slipstream over the fins. The RP-3 was only effective when its 60-pound warhead hit the target.[13]

A Sherman Firefly crosses 'Euston Bridge' over the Orne as it moves up to the start line for Operation Goodwood, 18 July 1944

Three different variants of Sherman Firefly served during the Second World War, each based on a different variant of the M4 Sherman. The Firefly conversion was carried out on Sherman I (M4), Sherman I Hybrid (M4 Composite) and Sherman V (M4A4) tanks. Some sources state that several Sherman IIs (M4A1) were converted and used in action, but photos allegedly showing these conversions are in fact views of the front half of Sherman I Hybrid Fireflies. 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.[14] The majority of Shermans converted were the Sherman V/M4A4 model, of which the British received about 7,200. The Sherman VC and IC variants are easily distinguished by their lower hulls; the VC having a lengthened hull, and larger gaps between the suspension units. They employed the three-piece bolted transmission housing. The Sherman IC usually had a cast transmission housing. The Hybrid can be distinguished by its upper hull, which is cast and gives it a distinctive curved look in comparison to the more boxy hull of a typical Sherman.

Production of the Firefly started in January 1944 and, by 31 May, some 342 Sherman Fireflies had been delivered to the 21st Army Group for the D-Day landings.[8] As a result, British tank troops were composed of three standard Shermans and one Firefly. The same distribution occurred in Cromwell units, but this caused logistical problems, as each Cromwell troop then needed to be supplied with parts for two different tanks. The Firefly was also slower than the Cromwell. Churchill units received no Fireflies, and as a result, often had to rely on any attached M10 or M10 Achilles units to provide increased firepower to deal with tanks their own guns could not eliminate.[3]

Production was limited by the availability of suitable tanks, with the phasing out of 75 mm Sherman production. To make up numbers, Sherman I and Sherman I Hybrids were also converted.[4] From D-Day in June to the end of the Battle of Normandy in late August, almost 400 Sherman Fireflies were converted, more than sufficient to replace any permanent tank losses during the battle.[15] 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.[3] By February 1945, some 2,000 Sherman Fireflies had been built and British, Commonwealth, and Polish armoured units were equipped with a 50/50 mix of 75 mm and 17-pounder-armed Shermans.

In the spring of 1945, production of the Firefly was scaled down, with the last tank being delivered in May 1945. This was the result of several factors, from superior home-grown designs like the Comet and Centurion coming into service to replace the Firefly, to the impending defeat of Nazi Germany, and the inferior design of Japan's tanks, which it seemed would be the next opponents the British would have to face after the fall of Germany.[8]

Production of the Sherman Firefly reached some 2,100 – 2,200 tanks; exact numbers are hard to determine as documents give contradictory totals.[8] Jane's World War II Tanks and Fighting Vehicles gives a production of 1,783 vehicles in 1944 and 563 in 1945, for a total of 2,346.[16] Sherman Firefly gives a number of 2,002 conversions made between January 1944 and February 1945[15] or a total of 2,139 conversions.[17]

• 
  A Firefly VC in Ursel Air Base, Belgium; gun barrel is painted with countershading pattern used to disguise length
• 
  Firefly VC of 1st Polish Armoured Division at the Tielt liberation monument
• 
  A Firefly IC Hybrid in the Dutch Cavalry Museum at Amersfoort

The Tank Museum at Bovington in the United Kingdom has a Sherman Vc.[29]

• M4 Sherman variants
• Lend-Lease Sherman tanks
• Allied technological cooperation during World War II
• ROF Nottingham (carried out conversion)
• Ordnance QF 75 mm

• Sigal Fogliani, Ricardo Jorge (1997). Blindados Argentinos, de Uruguay y Paraguay (in Spanish). Ayer y Hoy. ISBN 987-95832-7-2.
• Sigal Fogliani, Ricardo Jorge (2018). El Sherman en El Ejercito Argentino (in Spanish). Kanon Editores. ISBN 9789874112132. Retrieved 7 August 2021.

Wikimedia Commons has media related to Sherman Firefly.

• Sherman Firefly Book Homepage
• Camouflage of 17-pdr Gun Mounted in Sherman Tank