The British Mark V tank[note 1] was an upgraded version of the Mark IV tank. It was first deployed in 1918, used in action during the closing months of World War I, and in the Allied intervention in the Russian Civil Waron the White Russian side, and by the Red Army, after they were captured. The tank was improved in several aspects, chiefly the new steering system and engine, but it fell short in other areas such as mechanical reliability and its insufficient ventilation. However, the Mark V was successful, especially given its limited service history, and primitive design.
The Mark V was, at first, intended to be a completely new design of tank, of which a wooden mock-up had been completed; however, when the new engine and transmission originally planned for the Mark IV became available in December 1917, the first, more advanced Mark V design was abandoned to avoid disrupting production. The designation "Mark V" was switched to an improved version of the Mark IV, equipped with the new systems. The original design of the Mark IV was to have been a large improvement on the Mark III, but had been scaled back due to technical delays. The Mark V thus turned out very similar to the original design of the Mark IV – i.e. a greatly modified Mark III.
Production of the Mark V started at Metropolitan Carriage and Wagon at the end of 1917; the first tanks arrived in France in May 1918. Four hundred were built, 200 Males and Females; the "Males" armed with 6-pounder (57 mm) guns and machine guns, the "Females" with machine guns only. Several were converted to Hermaphrodites (sometimes known as "Mark V Composite") by fitting one male and one female sponson. This measure was intended to ensure that female tanks would not be outgunned when faced with captured British male tanks in German use, or the Germans' own A7V.
The Mark V was to be followed by the more advanced Tank Mark VI, but this was abandoned in December 1917, to ensure sufficient production by British, American, and French factories of the Tank Mark VIII for a planned 1919 offensive. However, the war ended in November 1918, and few Mark VIIIs would be built (most of those completed in Britain were immediately scrapped). The Mark V was also the basis of the Mk IX Troop Carrier, a dedicated Armoured Personnel Carrier, but only 34 were completed by the end of the war. After the war, most of the British Army's tank units were disbanded, leaving five tank battalions equipped with either the Mark V or the Medium Mark C. The British Army's interest shifted more to lighter, faster tanks, and the Mark V was partially replaced by the Vickers Medium Mark I during the mid-1920s. Although the Vickers Medium Mark I was heavier Vickers A1E1 Independent reached prototype stage in 1926, but it was abandoned for lack of funds. The remaining Mark Vs appear to have been replaced by medium tanks by the end of the decade.
In early 1917, some British tanks were tested with experimental powerplant and transmissions ordered by Albert Stern. These included petrol-electric schemes, hydraulic systems, a multiple clutch system, and an epicyclic gearbox from Major W.G. Wilson. Though the petrol-electrics had advantages, Wilson's design was capable of production and was selected for use in future tanks.
The Mark V had more power (150 bhp) from a new Ricardo engine (also ordered by Stern). Use of Wilson's epicyclic steering gear meant that only a single driver was needed. On the roof towards the rear of the tank, behind the engine, was a second raised cabin, with hinged sides that allowed the crew to attach the unditching beam without exiting the vehicle. An additional machine-gun mount was fitted at the rear of the hull, this placed the engine in the center of the cabin.
The Ricardo engine was still in the centre of the crew compartment which led to miserable crew conditions from its heat output. The noise also interfered with crew communication.
The second problem with the Ricardo engine was related to its reliability, or lack thereof. The Ricardo engine was of a somewhat unorthodox design, but it was highly efficient and, with proper care and attention, most of the issues could be mitigated. However, during combat proper maintenance, while important, was the least of the crew's concerns.
The ventilation was the area in which the Mark V suffered its largest weakness. The previous Marks I-IV drew cooling air from inside the tank, through the radiator, and then expelled the air through a vent, which provided a constant supply of moving air for the crew. In contrast, the Mark V, drew air from outside the tank, across the radiator, and then expelled the air though a vent, which left the air inside the crew compartment stagnant. The only ventilation for the crew compartment, other than the driver and gunner view-ports, located on all sides of the tank, was a roof-mounted Keith fan. This fan was inadequate for maintaining a stable supply of clean air for the crew of a Mark V; exhaust and gun-smoke were trapped with the crew, which caused many crewmen to grow ill and, in the most extreme cases, was enough to render them unconscious; either way the crew was practically unfit for combat within a few hours.
In an attempt to stop the tank threat, the German Army began digging wider trenches that made it difficult for tanks to cross. For example, trenches in the Hindenburg Line were widened to 11 or 12 feet, which was more than the British tanks' 10 feet trench-crossing ability. To counter this, Sir William Tritton developed the Tadpole Tail, an extension of the tracks to be fitted to the back of a tank, this lengthened the tank by about 9 feet. It was also hoped that this longer tank might carry a squad of infantry with Vickers or Lewis machine guns, but the conditions inside were so extreme that the men became ill, after some early experiments, and although several hundred were manufactured, the idea was abandoned. This in turn caused Major Philip Johnson of the Central Tank Corps Workshops to devise a plan of his own. He cut a Mark IV in half and inserted three extra panels, lengthening the hull by six feet. (It was believed for a long time that most Mark V* had been field conversions made by Johnson. It is now known that they were all new, factory-built to a new design). The V* had a reshaped rear cupola incorporating 2 extra machine-gun mounts, a door in each side of the hull, with an extra machine-gun mount on each. This tank weighed 33 tons. The total orders for the Mark V* were 500 Males and 200 Females, 579 had been built by the Armistice – the order was completed by Metropolitan Carriage in March 1919. Shortly before the end of the War, Britain supplied France with 90 Mk V*. They were not used in action, but remained in French service throughout the 1920s and 30s.
A British Mark V* tank
—on the roof the tank carries an unditching beam
on rails, that could be attached to the tracks and used to extricate the vehicle from difficult muddy trenches and shell craters
Note: the asterisk (*) in early British tank designations was usually pronounced as "star" when spoken, e.g., Mark Five-star, or Mark Five-star-star, etc.
Because the Mark V* had been lengthened, its original length-width ratio had been spoiled. Lateral forces in a turn now became unacceptably high causing thrown tracks and an enormous turning circle. Therefore, Major Wilson redesigned the track in May 1918, with a stronger curve to the lower run reducing ground contact (but increasing ground pressure as a trade-off) and the tracks were widened to 26.5 inches. The Mark V engine was bored out to give 225 hp and sited further back in the hull. The cabin for the driver was combined with the commander's cabin; there now was a separate machine gun position in the back. Of a revised order for 700 tanks (150 Females and 550 Males) only 25 were built and only one of those by the end of 1918.