British Mark1 and 1a Tank

 The Mark 1 medium tank was introduced in 1924 as the first postwar British design and was a radical departure from the WW1 tanks. A 3 lb gun occupied the turret and the 90 hp aircooled V8 was mounted in the front left corner. 114 gallon of gas were carried for a range of 120 miles.
 Five Mark IAs were produced, with the designations A4E6 to A4E10. Like the Mark Is they were used for experimental purposes. The A4E10 was used to test a two-gun armament, with a .5 inch Vickers machine gun mounted above the .303 gun. Another was used to test the Ricardo 65hp engine, and a third to test a different suspension system that didn't require the rear idler wheel. Four of the five Mark IAs were sent to India in 1931 for tropical trials. These tanks were given square bevel sided non-rotating cupolas at the Base Workshops at Chaklala, and were also used to test different methods of reducing the temperature inside the tank. The most successful of these involved the use of an asbestos fabric lining. The Mark IA was followed by the Mark II, the first version to be produced in significant numbers.