Chyetverikov MDR-6

The Chyetverikov MDR-6 was a 1930s Soviet Union reconnaissance flying-boat aircraft, and the only successful aircraft designed by the design bureau led by Igor Chyetverikov.
Development.
First flying in July 1937, the MDR-6 was a two-engined high-wing monoplane of all-metal stressed skin construction. The prototype was powered by two M-25 radial engines. A production run of 20 units powered by M-63 engines were produced in 1940 and 1941. All the aircraft were withdrawn from service in 1942 due to structural problems.
Several progressively advanced prototypes were built from 1939 to 1945, but no further production ensued.