This was a copy of a 3.7 cm (1.5 in) German weapon designed by Rheinmetall that was sold to the Soviets before Hitler came to power in 1933 that had been enlarged to 45 mm (1.8 in) to reuse a large stock of old 47mm ammunition.

However it was not very effective as its slow rate of fire and lack of a time fuze required a direct hit to damage targets.

Its semi-automatic breech automatically ejected the cartridge case and locked open, ready for the next round.

This was less than ideal for an anti-aircraft weapon that relied on its rate of fire to inflict damage on aircraft because every round had to be hand-loaded.

[1] Fully automatic weapons of roughly this caliber like the 40 mm Bofors typically used 4-5 round clips of ammunition to produce rates of fire four times as high.