T-26 - Design

Design

The Soviets did not simply replicate the Vickers Six-Ton. Like its British counterpart, the T-26 mod. 1931 had a twin-turreted configuration and was designed to carry two machine guns, mounting one in each turret. A major difference between the Soviet T-26 mod. 1931 and the British 6-Ton were higher turrets on the T-26, complete with observation slit. Also Soviet turrets had a round firing port for the DT tank machine gun, as opposed to the rectangular ports used by the original British design for the Vickers machine gun. The front part of the hull was also slightly modified.

Hulls of twin-turreted T-26s were assembled using armoured plates riveted to a frame from metal angles. Some tanks, produced in 1931, had sealing zinc shims at the hull bottom at the interface between armoured plates for fording water obstacles. After experiencing problems with precipitation entering the engine compartment, a special cover was installed over an air outlet window after March 1932. A number of T-26s produced at the end of 1932–1933 had a riveted and welded hull. The T-26 mod. 1931 had two cylindrical turrets mounted on ball bearings; each turret turned independently through 240°. Both turrets could provide common fire in front and rear arcs of fire (100° each). The disadvantage of such configuration was impossibility to use all tank firepower at once on the same side. Four technological modifications of turrets existed, and they were mounted on tanks in different combinations (for instance, a tank with a riveted hull could have riveted and welded turrets).

The hull and turrets of the T-26 mod. 1931 had a maximum armour thickness of 13–15 mm (until 1938, see below), which was sufficient to withstand a light machine gun fire. Nevertheless, many twin-turreted tanks of the first series had 10 mm armour plates of low quality, which could be penetrated by 7.62 mm armour-piercing bullets from 150 m.

In 1933, the Soviets unveiled the T-26 mod. 1933. The Model 1933, with a new single cylindrical turret carrying one 45 mm cannon and one 7.62 mm machine gun, would become the most common T-26 variant. The 45 mm 20K tank gun was based on the Soviet 45 mm anti-tank gun 19K (mod. 1932). The T-26 could carry up to three secondary DT 7.62 mm machine guns in coaxial, rear, and anti-aircraft mounts. This increased firepower was intended to aid crews in defeating dedicated anti-tank teams, as the original machine gun armament had been found insufficient. The turret rear ball mounting for the additional DT tank machine gun was installed on the T-26 tanks from the end of 1935 until 1939.

The T-26 Model 1933 carried 122 rounds of 45 mm ammunition, firing armour-piercing 45 mm rounds with a muzzle velocity of 820 m/s (2,700 ft/s), or lower-velocity high-explosive munitions. Tanks intended for company commanders were equipped with a radio set and a hand-rail radio antenna on the turret (so called radio tanks). Later the hand-rail antenna was replaced with a buggy-whip antenna, because the Spanish Civil War and Battle of Lake Khasan demonstrated that the hand-rail antenna unmasked commander tanks for enemy fire.

The tank was powered by a T-26 90 hp (67 kW) flat row 4-cylinder air-cooled petrol engine which represented a Soviet full copy of the Armstrong Siddeley engine used in the Vickers 6-Ton. The engine was located in the rear part of the hull. In the beginning, Soviet-made tank engines were of bad quality; they were improved beginning in 1934. The T-26 (Armstrong Siddeley) engine did not have an over-speed limiter, which often resulted in overheating and engine valve breakage, especially in summer. A fuel tank for 182 L (40 imp gal; 48 U.S. gal) and an oil box for 27 L (5.9 imp gal; 7.1 U.S. gal) were placed alongside of the engine. The engine required top-grade petrol; the use of second-rate petrol could cause damage to the valve units because of engine detonation. From mid 1932, a more capacious fuel tank (290 L instead of 182 L) and a simplified oil box were introduced. An engine cooling fan was mounted over the engine in a special shroud. From spring 1932, the exhaust muffler was affixed by three clamps instead of two.

The transmission of the T-26 consisted of single-disk main dry clutch, a gearbox with five gears in the front part of the vehicle, steering clutches, final drives and band brakes. The gearbox was connected to the engine by a drive shaft passing through the vehicle. A gear change lever was mounted directly on the gearbox.

A tank suspension (for each side) consisted of two bogies, four rubber-covered return rollers, a track driving wheel and a track idler. Each bogie consisted of a cast box, four twin rubber-covered road wheels connected by balancing levers and two one-quarter elliptic leaf springs. The cast track driving wheel with removable sprocket ring was located in front, and the track idler with a crank lever tightener was located in the rear part of the vehicle. A track made from chrome-nickel steel was 260 mm (10 in) wide and consisted of 108-109 links.

The T-26 mod. 1931 did not have a radio set. A tank commander communicated with the driver by speaking tube, which was replaced with a signalling lamp in 1932. The T-26 was equipped with one fire extinguisher, a kit of spare parts tools and accessories (including a tank jack), a canvas stowage, and a tow chain fixed on the rear of the hull.

The T-26 could cross 0.75 m high vertical obstacles and 2.1 m wide trenches, ford 0.8 m deep water obstacles, cut 33 cm thick trees and climb 40° gradients. The T-26 proved to be easy to drive.

Beginning in 1937, there was an effort to equip many tanks with a second machine gun in the rear of the turret and an anti-aircraft machine gun on top of it, as well as the addition of two searchlights above the gun for night gunnery, a new VKU-3 command system, and a TPU-3 intercom. Some tanks had vertically stabilised TOP-1 gun telescopic sight. Ammunition stowage for the main gun was improved from 122 rounds to 147. In 1938, the cylindrical turret was replaced with a conical turret, with the same 45 mm model 1934 gun. Some T-26s mod. 1938/1939, equipped with radio set, had a PTK commander's panoramic sight.

In 1938, the T-26 was upgraded to the model 1938 version which had a new conical turret with better anti-bullet resistance but the same welded hull as the T-26 mod. 1933 produced in 1935–1936. This proved insufficient in the Battle of Lake Khasan, which took place in 1938, so the tank was upgraded once more in February 1939 to have an underturret box with sloped (23°) 20 mm side armoured plates. The turret featured an increase to 20 mm at 18 degrees sloping. This time it was designated T-26-1 (known as the T-26 mod. 1939 in modern sources). There would be subsequent attempts to thicken the front plate, but T-26 production soon ended in favor of other designs, such as the T-34.