The Heavy Tank Mark VIII (Liberty Tank or International) was originally meant to be a joint Anglo-American-French tank that would have been used in large numbers if the war had continued into 1919, but that was eventually built in small numbers in British and American versions.
In October 1917 Albert Stern, the head of the Mechanical Warfare Supply Department, was ousted after a series of complains from senior officers at the War Office. In compensation Winston Churchill, then serving as Minister of Munitions, gave Stern a new post, as Commissioner for Mechanical Warfare (Overseas and Allies) Department. His job was to arrange an agreement in which the British, French and Americans would all cooperate to produce a new heavy tanks, to be built at a new factory on France, using parts produced by all three countries. Stern gained the support of General John J. Pershing, commander of the American Expeditionary Force. He managed to get all three countries to agree to a scheme in which 1,500 tanks would be built in France, although the French soon dropped out, leaving the Americans and British.
Work on the Mark VIII began in 1917, as a British design. The original design was produced by Tennyson D'Eyncourt and Lt John G. Rackham, but the detailed design emerged after the Allied agreement. Two American officers, Major H.W. Alden and Major J.A. Drain, joined the team. Of the two Alden was a technical expert, and made a contribution to the new design.
The Mark VIII was a long narrow vehicle. The main part of the hull (excluding the sponsons) was 9ft wide and 34ft 2in long, making it almost four times longer than wide. The sponsons added another 3ft 4in to the width of the tank.
The Mark VIII was given wider tracks than earlier tanks, giving it a 69.5in wide tread between the two tracks - the gap between the tracks was thus smaller than the overall width of the tracks. The gap between the inner and outer track frames was also increased (previous changes had seen the track made wider but not the gap between the frames, meaning that the tracks overlapped their frames). The inner frame was reduced in size to increase the amount of space within the tank.
The new tank was to be powered by a V12 engine, preferably the new water cooled V12 American Liberty engine, in a tank version with cast iron cylinders. This provided 300hp, twice the power of the 150hp Ricado engine used in the Mark V. The engine was mounted at the rear of the tank, in a separate engine compartment. A bulkhead divided this off from the crew compartment. Sliding doors in this bulkhead allowed the engineer to get into the engine compartment if needed. The engine powered a two-way transfer box that drove two-speed epicyclics, which could be used to steer the tank, and give it two speeds going forwards or backwards.
Internally the Mark VIII was quite spacious. The drive sat at the very front, with an armoured vision hood on top of the front of the fuselage. Behind him the space was open, apart from a large ammo locker in the centre of the space. Above this was a superstructure that emerge above the tracks. This had a number of firing positions for machine guns, and a commander's look-out tower on top. The gunners and commander could stand on the ammo locker to use these positions.
The 6 pounder (57mm) main guns were carried in a new design of sponson, designed by Major Alden. This was hinged at the front, and could swing in at the rear to reduce the width of the tank and allow it to be transported by rail. Storage racks for 6 pounder shells were mounted around the guns.
The side doors were just behind the sponsons, each with a ball mounted machine gun. British tanks would carry one machine gun in each door and five in the superstructure (two at the front, one at the back, one on each side), and be armed with air cooled Hotchkiss machine guns. US tanks didn’t carry the side turret guns, and used water cooled Browning machine guns.
The original plan was for the British to built the frames, armour plate, tracks, track rollers, main guns and weapon mounts, the Americans to provide the Liberty engines, transmission and mechanical components, and the French to assemble the tanks at the new factory at Neuvy Pailloux.
The French withdrawal from the scheme meant that these plans had to be changed, as did the later arrival of the Liberty engine. The British placed an order 1,500 machines, split between the North British Locomotive Company and Beardmores (both in Glasgow) and Metropolitan in Birmingham. Only North British actually began production. They built one prototype, powered by a Rolls-Royce V12 engine, and twenty four production machines, using a V12 version of the Ricardo engine. The prototype and five production machines entered service, the rest appear to have been scrapped.
The first mild steel hull was completed in Britain in July 1918, and sent to the United States to have the engine and transmission installed. The war ended before production got under way, but early in 1919 the US army decided to order 100 tanks. These were to be built at the Rock Island Arsenal, using 100 sets of components purchased from Britain.
Before construction got under way the pilot was put through a series of tests. This revealed that the low mounted exhaust made the engine room floor too hot, and this was modified in production tanks.
The tracks were carried by 29 unsprung rollers on the lower section, a drive wheel at the rear, large idler at the front and a single return roller about half way along, where the sloping rear hull began.
The Mark VIII could carry a crew of eleven - driver, commander, two 6-pounder gunners, two loaders and five machine gunners.
Production of the Mk VIII got under way at Rock Island on 1 July 1919, and the last of the 100 tanks was completed on 5 January 1920. By the time it entered service the Mk VIII was already basically obsolete - its thin armour made it vulnerable to the new generation of anti-tank guns, and its slow speed limited its usefulness. Most were used on infantry training exercises, until the type was withdrawn from service in 1932, They remained in service as late as the outbreak of the Second World War in 1939, and some of them were then removed from storage and used for training in Canada.
The Mk VIII was used for a number of experiments. In 1920-25 it was used to test a stroboscopic vision device. This consisted of a fixed central section with a series of large view ports, covered by a rotating hood with a series of narrow vertical slots. As the slots rotated past the view ports, enough light got through to give the commander a 360 degree view. Work on the new device was abandoned in 1925, as it was too vulnerable to splash from machine gun fire getting into the slots.
In 1932 one Mark VIII had an air cooled Liberty engine installed for tests. As a result of these tests, air cooled engines were recommended for future tanks.
Production: 100 (US), 25 (UK)
Hull Length: 410.5in (34ft 2.5in)
Hull Width: 144in (12ft) with Sponsons out; 108in (9ft) with Sponsons withdrawn
Height: 123in (10ft 3in)
Weight: 86,900lb combat loaded
Engine: 338hp 12-cylinder Liberty engine
Max Speed: 5.5mph
Max Range: 40 miles (road)
Armament: Two Hotchkiss 6-pounder (57mm) Mark II guns, five .30in Browning machine guns (US)