 92 and Kirov Plant, possibly also by ""UZTM"" (Ural Heavy Machinery Building Plant).Production rate was slow because of more sophisticated construction compared to older guns and because of constant need to fix faults in the design.In 1936 only 10 pieces were produced, in 1937 - 417, in 1938 - 1,002, in 1939 - 1,503.