The resulting light quarter-automatic anti-tank gun was discovered to be unsatisfactory due to low mobility and reliability problems, and after a series of modifications (including the arrest of the project's chief designer on August 10, 1933, after several production defects were uncovered), was re-sent to army trials 26 December 1933.

The resulting semi-automatic improved version was known as "45 mm anti-tank gun M1934" (Russian: 45-мм противотанковая пушка образца 1934 года).

The tank gun modification Russian: 45-мм танковая пушка образца 1932/38 годов (20-К) was still in use in the first stage of the German-Soviet War.

During 1941-42, some surplus M1938 barrels were fitted to trailer carriages to replace the losses of anti-tank guns suffered in the opening stages of Operation Barbarossa.

It was not very effective in this role since it had to be loaded by hand, which kept its rate of fire down to about 25–30 rounds per minute, and its lack of a time fuze meant that it had to score a direct hit to damage its targets.