Once it was realized that the BT tanks didn't have sufficient armor or armament a new design was developed to be fast medium tank. In 1937 the Kharkov factory was ordered to design a new tank and the design work started in November 1937. The chief designer was Mikhail Koshkin and his deputy Alexsandr Morozov.
The A-20 had sloping sides and an angular turret that was small.
Tracks could be removed and could be run on just the wheels.
The chassis for the A-20 was based on the BT-7M.
Alexsandr Morosov was the designer of the V-2 diesel engine.
Nikolai Kucherenko and P. Vssihev designed the suspension for the A-20. The three rear pairs of wheels provided the drive for the A-20.
In 1939 a 76.2 mm gun was installed and it became the A-30. This was the same gun that was installed in the BT-7.
The A-20's turret was made from 25 mm / 1" thick rolled armor plate.
There was an attempt to place a short barrel 76.2 mm gun in the A-20's turret but it just didn't work as the turret ring couldn't absorb the recoil.
The hull had a V-shaped glacis plate and was angled at 60°. The A-20's hull also overhung the tracks with the sides angled at 25°.