The Vickers 6-Ton Tank or Vickers Mark E was a British light tank designed as a private project at Vickers. It was not purchased by the British Army, but was picked up by a large number of foreign armed forces and was copied almost exactly by the Soviets as the T-26. It was also the direct predecessor of the Polish 7TP tank. By the start of World War II it was the second most common tank design in the world after the Renault FT-17.

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 A with two turrets, each mounting a Vickers machine gun.
• Type B with a single two-man turret mounting a single machine gun and a short-barreled 47 mm cannon .

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.

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. During the Spanish Civil War the Soviet Union sent the T-26 to the Republican Army. The Italians, after suffering losses from Republican's T-26 during the battle of Guadalajara (1937), captured some of these tanks which served as a model for their M11/39 and M13/40 light/medium tanks.