The 17pdr gun, the most powerful of the British wartime anti-tank guns, was meanwhile fitted to the American Shermans in British service, a compromise which produced one of the most effective tanks of the war years. This 17pdr version of the Sherman was called the Firefly.
The British mounted their 17-pounder antitank gun—ballistically a rough equivalent of the German 88—in one out of four of their Shermans. In the weeks after D-Day, none of the alternatives proved optional. The 75mm gun was ineffective against German frontal armor at any but near-suicidal ranges. American crews quickly learned that the 76mm was second-rate. To make it better fit a Sherman turret, the Ordnance Department reduced the barrel by over a foot, correspondingly reducing muzzle velocity, ballistic effectiveness, and armor penetration. The Firefly was an excellent tank killer, but its long barrel stood out from the Sherman shorthorns, making it a distinctive and favorite target.
The major development in British service of the Sherman tank was the fitting of the 17pdr gun to a proportion of Shermans to provide the most powerfully armed British tank of the war. Known as the Sherman Firefly, the fitting of the 17pdr gun had been suggested in January 1943 as a safeguard against the failure of the Challenger programme, this latter tank proving, on trials, to have several shortcomings. Though there was some opposition to this idea at the Ministry of Supply, the British War Office insisted on a pilot conversion being produced. This was ready in November 1943 and in February 1944 the Firefly conversion was given full priority for service following delays and uncertainties with the Challenger, which prevented it being in service in time for Operation Overlord, the Normandy landings.
In the late part of 1943, it was decided to mount the British high velocity 17pdr gun on to the Sherman. To achieve this, the turret had to be slightly modified and the gun was mounted on its side and adapted for left-hand loading. The original trunnions were used with a new mounting, recoil and elevating gear. Since the 17pdr breech filled almost the whole turret, displacing radio equipment from the rear wall, an aperture was cut in the rear of the turret and an armoured box which also acted as a counterweight was welded on to accommodate the radio sets in a rear extension. An additional hatch for the loader was cut in the turret roof, since the gun breech obstructed his exit through the commander’s rotating roof hatch. To provide maximum stowage space inside the hull for the 17pdr ammunition, the hull gunner’s position was eliminated, the bow machine-gun was removed, the aperture plated over and an ammunition bin replaced the seat. Thus modified, stowage for 78 17pdr rounds was provided in the vehicle. Most Fireflies were converted from the Sherman V (US designation M4A4) mainly because the British had large Lend-Lease deliveries of this model, and the next most numerous was basically the Sherman I (M4). Of these a proportion were the late-production M4 type with combination cast and rolled upper hulls. A small number of M4A1 (British Sherman II), M4A2 (British Sherman III), and M4A3 (British Sherman IV) were also converted. Apart from giving the M4 series their own designation (ie, Sherman I, II, III, IV and V) the British also applied a suffix letter to the mark number to indicate the armament. ‘A’ indicated US 76mm gun on any model, ‘B’ indicated US 105mm howitzer and ‘C indicated British 17pdr.
The Sherman Firefly was the only British tank landing at Normandy which could take on the German Tiger and Panther tanks on anything approaching equal terms and proved a most successful expedient design. Initially Sherman Fireflies were issued on the basis of one per troop, due to the shortage of 17pdr guns available for fitting in tanks. By early 1945, however, the type was in service in more generous numbers. In late 1945, a Firefly turret was sent to APG for test firing mounted on a M4A3 chassis. It was evaluated for the US Army but not adopted for service.
“Fireflys” at Norrey
9 June 1944
Nine Sherman tanks including several “Fireflys” equipped with the 17-pounder, were being moved towards the front to reinforce the Reginas’ position in Norrey. As the tanks, from the Elgin Regiment, were making a detour in front of the village when they spotted the advancing Panthers. Catastrophically for the 3rd Panzer Company, the swing to the left, though protecting them from the 6-pounders in Norrey, exposed their flanks to the Shermans at not more than 1000 metres distance. The Canadian tanks deployed in a straight line and opened fire. A “Firefly” commanded by Lieutenant Henry hit the tank nearest the rail-line first. Adolf Morawetz thought he had struck a mine; “after a dull bang and shaking, as if the tracks had been ripped off, the tank came to a standstill.” After another bang, the ammunition for the MG-42 ignited and the Panther burst into flames. Before Morawetz desperately attempted to open the hatch he had just closed, he looked through his periscope and watched as the neighbouring Panther exploded ” throwing the turret into the air. Morawetz survived, but his tank and crew had been destroyed. Six other Panthers were quickly dispatched in the next four minutes. The survivors, including the badly burned crews who had bailed out of their destroyed tanks, fled back towards the underpass. The infantry were forced to join the men of the 2nd Company under the bridge, as an artillery barrage began to pound the area inflicting heavy casualties. The converging attack of the 1st Battalion of the 25th Panzer Grenadiers never materialized. The assault was a complete and total failure.
Sherman IC (Firefly): British designation for M4A1 re armed in Britain with 17pdr gun.
Sherman VC (Firefly): British designation for M4A4 re armed in Britain with 17pdr gun. Most Firefly conversions were on the M4A4 chassis. Hull machine gun (and gunner) deleted in all Fireflies to increase ammunition stowage.