The first Mark E was built in 1928 by a design team that included the famed tank designers John Valentine Carden and Vivian Loyd. The hull was made of riveted steel plates, 1 inch (25 mm) thick at the front and over most of the turrets, and about 3/4 inch (19 mm) thick on the rear of the hull. The power was provided by an Armstrong Siddeley Puma engine of 80–95 horsepower (60–70 kW) (depending on the version), which gave it a top speed of 22 mph (35 km/h) on roads.
The suspension used two axles, each of which carried a two-wheel bogie to which a second set of bogies was connected with a leaf spring. Upward movement of either set of bogies would force the other down through the spring. This was considered to be a fairly good system and offered better than normal cross-country performance although it could not compare with the contemporary Christie suspension. High strength steel tracks gave over 3000 miles (5000 km) of life which was considerably better than most designs of the era.
The tank was built in two versions:
Type B with a single two-man turret mounting a single machine gun and a short-barreled 47 mm cannon OQF 3-pdr Gun.
The Type B proved to be a real innovation, it was found that the two-man turret dramatically increased the rate of fire of either weapon, while still allowing both to be fired at the same time. This design, which they referred to as a duplex mounting, became common on almost all tanks designed after the Mark E.
The British Army evaluated the Mark E, but rejected it, apparently due to questions about the reliability of the suspension. Vickers then started advertising the design to all buyers, and soon received a trickle of orders eventually including USSR, Greece, Poland, Bolivia, Siam, Finland, Portugal, China and Bulgaria. A Thai order was placed, but taken over by the British when the war started. Vickers built a total of 153 (the most common figure) Mark E's.
Experience with the Polish machines showed that the engine tended to overheat due to poor airflow over the air-cooled Puma engine. This was addressed by the addition of large air vents on either side of the hull. For a new Belgian order the design was modified to use the Rolls-Royce Phantom II water-cooled engine instead. This engine would not fit in the rear, and had to be mounted along the left side of the tank, requiring the turret to be moved to the right and rearward. One example of the resulting Mark F was tested by Belgium, but rejected. Nevertheless the new hull was used, with the older engine, in the sales to Finland and Siam.
The Mark E was also developed as a cargo vehicle, and purchased by the British Army in small numbers as artillery tractors to haul their large 60 pounder (127 mm) artillery guns. Twelve were ordered by the Army as the Dragon, Medium Mark IV, while China purchased 23 and India 18.
Poland was not happy with the design, purchased 50 and licensed it for the local production, but only put together 38 out of 50, using the unassembled 12 for spare parts. The Poles modified it with larger air intakes, their own machine gun, 360-degree Gundlach periscope. and 5 or more with two—way radios and decided to make their own tank that would address the shortcomings of the very Vickers: in the case of a 7TP, in fact nearly 10 tons heavy, the Poles also, besides the before—mentioned telescope, added liquid—cooled Diesel engine as well as better armor protection, better ventilation, two—way radios, 37 mm Polish version of Bofors anti—tank gun, and a bigger crew compartment. Out of 38 original two-turreted tanks, 22 were later converted to single turret version with a modified turret and the 47 mm main gun (Type B standard). The tanks were in bad shape by 1939 because they were used in the training units over period of five years. However, they did perform well and better than Renault R35, amongst others as part of the Polish 10. Cavalry Brigade in the Polish Defensive War in 1939.
The Soviets were also happy with the design and licensed it for production. However in their case local production started as the T-26, and eventually over 12,000 were built in various versions. The Soviet early twin-turret T-26s had 7.62 mm DT machine guns in each turret, or a mix of one machine gun turret and one 37 mm gun turret. Later, more common versions mounted a 45 mm gun and two DT machine guns. The final versions of the T-26 had welded construction and, eventually, sloped armor on the hull and turret. Because the T-26 was in such wide use and was a reliable platform, a variety of engineer vehicles were built on the chassis, including flamethrowers and bridgelayers. A novel radio-controlled demolition tank was built on the T-26 chassis also.