The Heavy Assault Tank, A39, Tortoise was one of the largest armoured vehicles produced in Britain during the Second World War, and proved to be surprisingly reliable, but at the same time utterly impractical.
The Tortoise emerged from a series of designs produced by Nuffield Mechanizations and Aero of Birmingham. The first of these, on 13 May 1943, was for a fairly small tank (similar to the Valiant Infantry Tank), and may have been produced to the same specification, but after that Nuffield produced an impressive series of sixteen designs of ever increasing size. In general each was larger than the last, while the armament changed repeatedly. Internally the designs were known as the Assault Tank (AT) series. By the time Nuffield reached AT13 the tank was armed with a 17-pounder gun, and by AT15A it had 9in of frontal armour and weighed 65 tons. Only the very first actually carried a normal turret.
The first official acknowledgement of the design came on 23 December 1943, when the Tank Board commented that a 68 ton tank with a 17-pounder gun wasn't justifiable. The Board suggested that a 3.7in gun should be used instead.
On 5 February Nuffield submitted design AT16. This was for a 72 ton tank armed with the 3.7in anti-aircraft gun (called the 37-pounder in this form), mounted in a cast housing in the front of the tank. Perhaps rather surprisingly the War Office accepted this design, which ignored all of the weight and width limits normally imposed on British tanks. The design was given the General Staff designation A39 and named the Tortoise. An order for 25 production tanks was placed on February 1944 and confirmed in May 1944. Deliveries were to start in September 1945. The order was reduced to 12 at the end of the war, and to 6 in 1945, of which five were delivered.
The A39 was a vast vehicle. To the top of the tracks it perhaps resembled the Churchill, with comparatively small road wheels (with sixteen bogies on each side) hidden behind an armoured shield, and a horizontal top. It had double torsion bar suspension and extremely wide 36in tracks. The superstructure resembled a massive but fixed gun turret, taking up the middle of the superstructure and filling almost the entire width of the vehicle. The superstructure was made from a single casting.
By the time the first Tortoise was complete it was armed with a 32 pounder gun, produced by modifying the original 37 pounder. The gun was mounted on a ball mount. Secondary firepower was provided by two Besa machine guns in a rotating cupola at the back-right of the superstructure, given stop guards to prevent these guns hitting key parts of the top of the tank (or firing too close to the crew hatches). It was powered by a Meteor engine, with a Merritt-brown combination gearbox and steering system.
The A39 Tortoise eventually weighed 78 tons. After the war it underwent trials, despite no longer being required. These rather unsurprisingly demonstrated that it was very difficult to actually transport the tank (with an almost impressively low cross country speed of 4mph!), but more surprisingly also revealed that it was a reliable design. It was also an excellent gun platform, and the 32-pounder accurate and hard-hitting.
Some documents refer to a Tortoise Mk II, to be powered by an unspecified 1,000hp engine, but little is known about that design.
Length with gun: 33ft
Hull Length: 23ft 9in
Hull Width: 12ft 10in
Crew: 7 (commander, driver, co-driver, gunner, machine gunner, two loaders
Weight: 174,720lb combat weight
Engine: 600hp Rolls-Royce Meteor V12
Max Speed: 12mph road, 4mph cross country
Armament: One 32pdr OQF, three 7.92cal Besa machine guns