Konstantin Alexievich Kalinin patented a wing of elliptical form in 1923, and in 1925 built the K-1 (RBZ-6), a small high-wing monoplane. Most notable developments were the K-4 (22 built) and the scaled-up K-5 (260 built, 1930- 1934). K-5, typically an eight-seater, made a significant contribution to Russian civil aviation. K-7 was an exceptionally large experimental bomber of 1933, having two faired underslung tandem-wheel landing-gear units and six engines. K-12 and K-13 were also bombers. In all, Kalinin designed 16 types before his bureau was disbanded in 1938.
In 1938 the arrest of Kalinin on trumped up espionage and sabotage charges, led to his execution.