The Spanish Civil War (1936-1939) proved as much a learning experience to the Soviets as it did to the Germans. At the time, the T-26 Light Tank and BT series of "Fast Tanks" made up the heart of the Red Army armored corps but these vehicles proved highly susceptible to enemy fire in direct contact battles, their gasoline engines lighting up the tanks (and crews within) when hit. This failing was further driven home in the Soviet-Japanese border war concerning Manchuria during 1938-1939 as Soviet gasoline-fueled tanks squared off against Japanese diesel-fueled ones.
No longer content with modifying existing designs of foreign origination, armored warfare through these experiences left the Soviets with the need to experiment on new indigenous tank designs. Back in October of 1937, Army authorities were already calling for a diesel-powered, well-protected, high-performance vehicle to feature up to 25mm thick armored facings. Like the BT series, this new development would have to be able to run on its roadwheels (sans tracks) as well as use the typical track-and-wheel drive arrangement. Primary armament would have to be either the proven 45mm anti-tank gun or the larger-caliber 76.2mm Soviet offering.
The A-20 Prototype
The Locomotive Works, Factory No.183 of Kharkov took on the optimistic project and drew up plans for an armored vehicle fitted with the 500 horsepower W-2-34 diesel-fueled unit mounting a 45mm main gun. Four road wheels are positioned to each hull side with three of these receiving drive power from the diesel engine and one axle being made steerable (for when running on its road wheels, sans tracks). This design became the "A-20" prototype. Armor protection reached 20mm. Sloped armor research, proven critical to basic ballistics protection, conducted through the BT-IS and BT-SW2 initiatives helped influence the armor arrangement of the new tank.
In essence, the A-20 was a further evolution of the BT - the drastic difference being the angled faces of its armor scheme which promoted a pyramidal shape when viewed from the forward profile. The turret remained in a forward-set position with the engine at rear and the track links were wide to promote better ground pressure in soft terrain. Total weight was 20 tons (US Short) and dimensions included a running length of 5.7 meters, a beam of 2.6 meters, and a height of 2.4 meters. Inside was a crew of four to include a driver, commander, gunner, and machine gunner.
Top achievable road speeds reached 40 mph on tracks and up to 47 mph on road wheels (on prepared roads). Range was out to 250 miles on tracks and 560 miles on road wheels.
With primary armament being the 45mm 20K L/46 anti-tank gun, the vehicle was fitted with a 7.62mm DT machine gun in a coaxial mounting for secondary, anti-infantry fire. The bow also contained an additional 7.62mm DT machine gun as an anti-infantry measure.
The A-32 Prototype
Not content with the A-20 in its current state, engineer Mikhail Koshkin took the same design and evolved it by way of enlarged dimensions (6m x 2.6m x 2.4m) which resulted in an extra road wheel to each hull side being added. The roadwheel-running quality of the A-20 was dropped for simplicity and a reduced maintenance commitment and armor was further increased to 30mm at the most critical facings. The primary armament was the larger-caliber 76.2mm gun while retaining both secondary 7.62mm DT machine guns in their place. All these changes came at a price for the vehicle's combat weight increased accordingly to 21 tons (US Short).
A-20 and A-32 Review
The plans for both vehicles were put on display for Soviet authorities during May of 1938 and some continued to champion the idea of a fast-moving tank that could run freely on its roadwheels while others saw the value of a slower, well-armored and armed tank to thoroughly defeat the enemy head-on. Stalin himself approved both forms for construction and this work began in February of the following year. By May, the drivable vehicles were made ready for the rigorous testing phase. Finalized forms of each were then thoroughly reviewed by authorities in September of 1939 - the same month that would see the beginning of World War 2 (September 1st, 1939).
In the State review and trials process, the A-32 was found to offer much more than the now-limited A-20: the road wheel drive function was no longer a prerequisite of future Soviet tanks and the shift-in-thinking to armor and firepower over speed finally took hold in the ranks. By this time, 45mm thick armor was being requested by the Army and the A-32 proved the superior candidate. Now given the more potent L-11 L/30.5 main gun, the A-32 design was constructed in two working prototypes - setting the stage for what would become the war-winning T-34 Medium Tank. The T-34 would carry-over many of the excellent qualities of the A-32 including its thick, sloped armored facings and a long-barreled main gun - its effect on the war would prove greater than any other tank, pulling the Soviets out of the brink towards a path to victory, a path that would run squarely to the doors of Berlin itself.
Meanwhile, the sole, abandoned A-20 prototype saw its last days in December of 1941 where it was used, and subsequently heavily damaged, in the desperate (yet successful) defense of Moscow.