The Kamov Ka-25 (NATO reporting name ‘Hormone’) was a naval helicopter, developed for the Soviet Navy in the USSR from 1958. Designed to meet a 1957 Soviet navy requirement for a new shipborne Anti-Submarine Warfare (ASW) helicopter, the first member of the Ka-20/25 family was the Ka-20 Harp, which initially flew during 1960. The production Ka-25BSh Hormone-A was of near identical size and appearance, but was fitted with operational equipment and uprated GTD-3F turboshaft engines (from 1973 these were replaced by GTD-3BMs). It entered service with the Soviet navy in 1967.
It was the first Soviet helicopter, developed specially for maritime use. Its coaxial design with lack of a tail rotor gave the helicopter smaller dimensions and reduced footprint on ships.
Although the lower part of the fuselage was sealed and watertight, the Ka-25 was not intended for amphibious operations, and flotation bags were often fitted to the undercarriage for use in the event of a emergency landing on the water. The cabin was adequate for the job, but was not tall enough to allow the crew to stand upright. Progressive additions of new equipment made the interior more cluttered.
It has been estimated that some 260 of the 450 or so Ka-25s produced were Hormone-As. After collapse of the Soviet Union a number of helicopters were passed on to Ukrainian Navy. By 2010 only a handful remained in Russian and Ukrainian service, mostly fulfilling secondary roles. Small numbers of Ka-25BShs have been exported to Bulgaria, India, Syria, Vietnam and former Yugoslavia. These ASW helicopters were replaced by the newer Ka-27 and its export version, the Ka-28.