The Mark VI was a British heavy tank

Tank

A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...

 project from the First World War.

After having made plans for the continued development of the Mark I into the Mark IV, the Tank Supply Committee (the institute planning and controlling British tank production) in December 1916 ordered the design of two new types: the Mark V and the Mark VI. The Mark V should embody the most advanced features that could still be incorporated into the Mark I hull. The Mark VI should abandon the old hull entirely, reflecting only some general principles of the older tank.

On 13 July 1917 Metropolitan

Metro Cammell

The Metropolitan Cammell Carriage and Wagon Company was a Birmingham, England based manufacturer of railway carriages and wagons, based in Saltley and subsequently Washwood Heath....

, the firm associated to Sir William Tritton

William Tritton

Sir William Ashbee Tritton, M.I.Mech.E., J.P. was an expert in agricultural machinery, and was directly involved, together with Major Walter Gordon Wilson, in the development of the tank...

, had a wooden mock-up ready of both types each. As no design drawings of the Mark VI have survived, the pictures made on that date (and on an earlier occasion on 23 June of the still partly unfinished models) form our major source of information.

The Mark V design still looked a lot like the Mark I. It had many detail changes however, including smaller sponson

Sponson

Sponsons are projections from the sides of a watercraft, for protection, stability, or the mounting of equipment such as armaments or lifeboats, etc...

s with cylindrical machine gun

Machine gun

A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....

 mounts, lengthened hull, larger cabin and a machine gun position at the back. This design was ultimately abandoned due to enormous delays in the development of the Mark IV. The tank taken in production under that name was not the Mark IV as originally planned but basically a slightly changed Mark I. When at last in December 1917 the desired new engine and transmission could be built in, it was this type that was now called the Mark V.

The Mark VI design had a completely different hull, much higher with rounded tracks on front. It had no sponsons; the side doors replacing them having machine gun positions. The main armament is a single 57 mm gun low in the front of the hull. The driver is sitting in a square superstructure much further back, the corners of which each had a machine gun

Machine gun

A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....

. We know from a surviving text that the hull was to be compartimentalised with a separate engine room on one side containing also in line the drive gears of both tracks, the drive shaft for the track of the opposite side crossing the hull. Wider tracks (75 cm) were to be used.

When in September 1917 US headquarters in France decided to create a separate American Tank Corps with 25 battalions among which five Heavy Tank Battalions, Major James A. Drain ordered 600 of the most advanced British tank, being at the time the Mark VI. However this endangered the plans of Albert Gerald Stern

Albert Gerald Stern

Sir Albert Gerald Stern was a banker who became the Secretary of the Landships Committee during World War I, where his organisational ability and influence in financial circles assisted the Committee in creating the first British tank....

, then coordinating allied tank production, to produce a common Anglo-American tank, the Mark VIII

Mark VIII (tank)

The Tank Mark VIII or Liberty was an Anglo-American tank design of the First World War. Initially intended to be a collaborative effort to equip France, the UK and the US with a single tank design, it did not come to fruition before the end of the war and only a few were produced.-Early...

. In December 1917 he ordered to halt the project. Not even a prototype was built.