Back to the Drawing Board: A39 Tortoise Heavy Assault Tank

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David Porter on military history’s doomed inventions

A prototype of the Tortoise, which proved in testing to be a ‘dead-end’.
A prototype of the Tortoise, which proved in testing to be a ‘dead-end’.

The Tortoise originated with a requirement issued in April 1943 for a well armoured assault vehicle that could break through heavily defended areas. The intention was that it should become one of ‘Hobart’s Funnies’, the specialist AFVs operated by 79th Armoured Division in support of other formations.

Nuffield Mechanizations Ltd carried out a series of 18 design studies to meet the requirement. Initially, these were for relatively modest tanks of 36 tons, but the constant improvements in German AFVs and anti-tank weapons forced a steady increase in armour and armament. By February 1944, the design had grown to 72 tons, armed with the new 32-pdr gun and three Besa machine-guns.

This design was approved, and 25 vehicles ordered that were to be operational by September 1945. Production of these huge vehicles, whose weight had now crept up to 78 tons, was a slow business, and with the end of the war the order was reduced to six.

A single example was sent to Germany for automotive and gunnery trials in 1947/1948. Its 650hp Rolls-Royce Meteor engine gave a road speed of 12mph, dropping to 4mph cross-country. Fuel consumption was staggering, giving a range of no more than 45 miles on roads and a miserable 25 miles cross-country. Although the torsion-bar suspension gave a very smooth ride, even over rough terrain, it had 200 separate lubricating points, creating a maintenance nightmare.

Getting into battle

While battlefield mobility was surprisingly good, getting the Tortoise to the battlefield would have been a major challenge. The trials showed that road movement of a single tank needed a special 80-ton tilt-bed trailer, towed by two 12-ton Diamond T tank transporters. Its sheer bulk and weight meant that rail transportation was impossible, and it far exceeded the capacity of any landing craft or standard Bailey bridges.

What was not in doubt was the amazing power of the 32-pdr, an anti-tank weapon derived from the 3.7-inch AA gun. It was fitted in a large ball mounting in the hull front, protected by a large armoured collar. This allowed powered traverse of 40º left and right, with elevation/depression of +20/-10º. Sixty rounds of 32-pdr ammunition could be stowed in the roomy fighting compartment.

Firing trials showed that its standard armour-piercing rounds easily penetrated a Panther’s frontal armour at a range of 950 yards. A subsequent shot against the same target at 1,350 yards tore away the lower section of the gun mantlet, before being deflected downwards through the roof armour above the driver’s position and ending up under the turret floor.

Unlike many similar German and Soviet designs, Tortoise was well-armed against infantry anti-tank teams. Its secondary armament comprised three Besa machineguns, two in a small turret on top of the hull, with the third in a ball mounting to the left of the 32-pdr. The turret-mounted guns had to be hastily fitted with safety cut-outs to prevent accidental firing at the roof hatches.

The trials confirmed that Tortoise was a ‘dead-end’ in AFV design. Most of the handful completed were scrapped or used as targets on firing ranges. A single fully restored survivor is on display in the Tank Museum at Bovington.

This is an article from the April/May 2021 issue of Military History Matters. To find out more about the magazine and how to subscribe, click here.

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