In 1917 Sir William Tritton had developed the Medium Mark A Whippet without involving his former co-worker Walter Gordon Wilson.

In response Major Wilson began to design an improved type on his own, the Medium Mark B, in July 1917.

At first 200 tanks were ordered; later this was increased to 600, all to be produced by William Foster & Co Ltd at Lincoln with Armlet & Wortley as subcontractor.

[3] It too has the general rhomboid shape of the Mark I and later heavy tanks combined with a fixed armoured structure, or casemate, well forward,[4] fitted with ball-mounts for five machine guns.

A fuel tank holding 150 imp gal (680 L) of petrol allowed for a range of 140 mi (230 km).

In the (likely) eventuality that the Medium Mark D would not be ready for mass production in 1919, the Tank Corps hoped to receive no fewer than 6,000 Medium Cs that year, a third of which would be of the "Male" version, with a long six-pounder (57 mm) gun, as used on the first British tanks, in the front of the superstructure.

As it was the most modern materiel of the Tank Corps, it was carefully kept from harm: no Medium C's were sent either with the Expedition Forces against the Bolsheviks in Russia or to the Anglo-Irish War.