Other improvements comprised semi-automatic breech, sight, firing button, suspension, reliable shield mount, and movable part re-balancing.

The sum of evolutionary improvements resulted in a significantly different design to justify the new factory code (53-K).

A further experimental series of 6 pieces were built in November 1937, which bore a number of improvements from the original design.

The 3rd gun (barrel number 0734) was sent with a Ya-3 limber was sent to the NIAP, arriving on 28 January, having already fired 605 shots during factory tests.

The guns fired on average 450 shells without failures, and traveled from Moscow via Kharkov to Krasnodar.

Richard Baxell notes that the gun in Spain "was effective against even heavy tanks at distances of up to three kilometers.

"[3] The guns also saw service in first stage of the German-Soviet War, but their anti-armor capabilities allowed them to fight successfully only with German light tanks and armored personnel carriers.

Ammunition types: Media related to M-37 45 mm anti-tank gun at Wikimedia Commons