Even though the Medium Tanks Mk.I and Mk.II were well designed, the military had complaints regarding them. The front mounted engine impacted the driver's visibility. The top speed of the tanks was also unsatisfactory. 24 kph was enough for the 1920s, but the military's expectations grew. This makes sense: there is no such thing as a tank that's too fast, and improving a tank's speed can only improve the tank's fighting qualities.
The new medium tank concept did not come from nothing. Oddly enough, its progenitor was a heavy tank. In 1922, the Ministry of War compiled requirements for a heavy tank. According to them, the tank had to have a low silhouette, rear engine, and the ability to cross 2.8 meter wide trenches. Its armament consisted of a 3-pounder (47 mm) gun and two machineguns in sponsons. The Vickers company joined the project, reworked it, and proposed the installation of the gun in a rotating turret. Eventually, that project turned into a completely different tank, known as the A1E1 Independent. Nevertheless, a tank with a rear engine, one cannon in a turret, and machineguns on the sides was not forgotten.