The Beriev Be-4 was the design bureau’s most modern amphibian at the start of World War II, and a successor to the mass produced MBR-2 that preceded it. The design was a strange mix of an aesthetically pleasing and modern-looking fuselage with an unconventional wing and engine configuration. This consisted of a parasol-wing mounted on a pair of struts and attached to a large M-62 radial engine which itself was mounted on a centrally mounted nacelle. The subtle inverted gull wings were also a defining characteristic of the aircraft. Performance of the Be-4 was much superior to its predecessor but suffered from lack of priority given to naval aircraft as well as disruption of production following the German invasion; just two aircraft were completed before its factory was dismantled and relocated to the Urals. In the event, only a few dozen were produced, which was barely a trickle compared to its predecessor. They mostly serving in the maritime patrol and anti-submarine roles in the Black Sea during 1943-45.

First flight of the KOR-2 took place on 21 October 1940, but the name was changed to Be-4 before entering production in 1941. No variants besides the standard production type were developed.