The Tank Museum | E1951.32

Tank Heavy Assault A39, Tortoise (E1951.32)

Tank Heavy Assault A39, Tortoise
vehicle info
Precise Name
Tank Heavy Assault A39, Tortoise
Main Utility Type
Tank Killer
Country of Use
1946/7, Nuffield Mechanisation & Aero Ltd., United Kingdom
Post War
location in the museum
The Tortoise project began in 1943 with the design of a turreted Assault Tank which was never built. This was followed by seventeen more designs, only one of which was built. Six prototypes of this version were built by the Lord Nuffield's company but they were not ready until 1947 so this huge machine played no part in the Second World War.

The gun in Tortoise was adapted from the famous 3.7 inch anti-aircraft gun and it is supported in a giant ball mounting. like an enormous gimbal, rather than conventional trunnions. This gun was capable of dealing with the most powerful German tanks of the war period and probably would have been a match for contemporary Soviet machines but it was too heavy and too slow for modern warfare.

Two of these machines were tested in Germany in 1948. They were difficult to transport and could damage roads and bridges but in firing trials the gun proved extremely accurate. However it was hard work for the loader, despite the fact that shell and shell case were loaded separately and there was considerable criticism of the ammunition stowage arrangements. Tortoise was never accepted for active service.

This particular vehicle was used in motion study (see 623.438.4(41) TORTOISE) and in firing trials at Larkhill in 1949 (see 623.438.4(41) TORTOISE).

Precise Name: Tank, Heavy Assault, A39, Tortoise

Other Name: AT17


The A39 Tortoise is the ultimate manifestation of the British concept of the heavily armoured, but slow, ‘Infantry’ tank. Conceived in 1943 some 17 designs were considered during its’ evolution before a configuration that was similar to the German turretless assault guns was decided upon. It appears from contemporary documents that Mr Duncan Sandys who was Secretary of State for War and Prime Minister Churchill’s son-in-law backed the project.

The design that was actually produced by Nuffield Mechanisation Ltd, AT17, was submitted in February 1944. It mounted a 3.7in (93.4mm) gun carried in a ball mount or gimbal in the hull front. This gun fired an Armour Piercing Discarding Sabot projectile at 3,600 feet/sec and proved to be very accurate and destructive. The gun was capable of penetrating all the German tanks of the late war period and would probably have been a match for contemporary Soviet tanks. The tank rode on 36in wide tracks and had a double torsion bar suspension. The superstructure was a massive single casting. The armour had a maximum thickness of nearly 9 inches (225mm) and the tank weighed a massive 78 tons. It seems that all the physical constraints that British tank designers had laboured under were discarded for this project! These included the limits due to the railway loading gauge, the strength of Bailey Bridges and the width of landing craft ramps. In practice the Tortoise proved to be too slow and unwieldy for the conditions of modern warfare and was a nightmare to transport.

Twenty five tanks were ordered in May 1944 and deliveries were expected to start in September 1945. However none had appeared by the autumn of 1945 and the order was reduced to 12 vehicles. The first tank finally appeared in 1946 by which time the War Office had lost interest in the project and in the end only five were manufactured.

The only service that the Tortoise had was when two tanks took part in trials in Germany in 1948. These showed that it was difficult to transport and could damage roads and bridges. The tank proved to be surprisingly reliable and the gun very accurate. However it was hard work for the loader despite the fact that the projectile and cartridge case were loaded separately, (the complete round weighed 45 lb.). There was also considerable criticism of the ammunition stowage arrangements.


The Universal tank. British Armour in the Second World War, Part 2. David Fletcher. ISBN 0 11 290534 X, HMSO, London 1993

Mike Garth

Painted on the vehicle are the letters JLR 98 in white Vehicle Audit 2019 Sighting equipment: 7 vision blocks present, 1 missing from front, 1 missing from rear
Periscope missing from machine gunner’s turret
5 vision blocks missing from driver’s position
Right periscope hood is missing, left is present
Internal Stowage Commander's position Inside of hatch brow pad held on by plastic, back of commander’s seat held on by plastic bags, leather is ripped and stuffing falling out. Brow pad ripped open stuffing is now on floor and one pad is missing.
Top of periscope and part of a vision block found in compartment
Signal cartridge box: empty, grenade box: empty, prism box: contains one handle, map case box: empty, Thompson sub-machinegun mounting: empty, box under seat: nuts and bolts
Generator missing button or dial
Metal plates loose on floor
5 x unidentified metal objects in ammunition racks
Gunner's position Machine gunner’s seat wrapped in plastic, bow gunner’s seat backrest and cushion is present, remainder of cushion in plastic bag, gunner’s seat folded and wrapped in plastic fittings for water bottle and bren gun are empty Driver's position Driver’s head rest wrapped in plastic , seat and backrest got plastic on
Left lever knob broken off and wrapped in gaffer tape
Brow pad for driver gaffer taped
Fire alarm connected to 2 fire extinguishers
Speedometer glass is shattered External stowage Rear left small stowage contains: one long brass rod, a homemade tool, gasket and a bit of exhaust pipe. Should contain: crowbar, pickaxe, sledgehammer, shovels, tank cleaning kit, wire cutters, wiring gloves
Rear left large stowage: empty. Should contain: bore cleaner, muzzle cover, breech cover, wood block, hemp rope.
Spare tracks on left hull
Rear right small stowage contains 3 x washers, wire, broken strap should have: biscuits and gas capes. Also one catch is broken
Inboard stowage: empty, should contain: engine tools, tank tools, tool kit, spare track links, cooker, collapsible bag, leaching powder.
Large inboard stowage: empty. Should have: blankets, great coats, brown sheets, staves and ends.
Hull right: towing cable, 20 litre Jerry can, spare tracks
Missing rear fire extinguisher
Infantry telephone on rear
Rear hatch missing two bolts
Missing side lights

Full Tracked
Gun - 32 Pounder (94 mm) Gun inscription: 32PR BX2
Armament - Main Weapon Type
3* 7.92mm Besa Machine Guns Turret Besa: mk.3 serial no. C40059, welded into gun mount missing second turret Besa Hull Besa: mk.3 serial no. C9540
Armament - Secondary Weapon Type
Rolls Royce Meteor Mark 5, 12 cylinder
6 speeds - each direction
Torsion bar
2 inch smoke mortars Missing
Armament - Secondary Weapon Type
Vehicle Statistics
Number (Crew)
Weight (Overall)
Maximum (Speed - Road)
Type (Fuel)
Maximum (Armour Thickness)
Calibre (Main Gun)
Power (Engine Output)
Volume (Fuel)
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Length (Overall)
Width (Overall)
Height (Overall)