Medium Mark D

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Medium Tank Mark D was a British medium tank developed at the end of World War I for Plan 1919, a big attack that aimed to break German defenses and disrupt their command. The war ended in 1918 before it could fight, but development continued for the post-war British Army. The project came from J. F. C. Fuller’s ideas, with Major Johnson at the Mechanical Warfare Department in Dollis Hill leading the design. It was built by Fowler, Vickers, and later by the Royal Ordnance Factory.

The tank was long and narrow, with a cylindrical front fighting compartment armed with three Hotchkiss machine guns. The driver sat at the back under a small cupola, and the roof sloped down to improve the view ahead. To keep the weight down while letting the suspension flex, Johnson used steel cable springs between the road wheels and tied the tracks with wire ropes so the suspension could flex during turns and rough ground. This unusual suspension proved troublesome and was eventually replaced in later designs.

Plan 1919 called for a speed around 20 mph, faster than many tanks of the time. Fuller even pressed for amphibious capability, asking that the design be able to swim. Two modified versions, the D* and D**, were built for swimming trials; the D* was widened, and the D** reached about 9 feet in width and performed well in river testing.

Although funds were approved for 45 tanks with Rolls-Royce engines, the project was cut back to 20, and only three were built by the Royal Ordnance Factory. These were built to the D Modified (DM) design, and Johnson’s work on the Mark D ended in 1923.

Note: this is not the same as the export Vickers Medium Mark D built for Ireland in 1929, which was a separate project.

In short, the Medium Mark D was an ambitious fast, potentially amphibious tank that never entered service.