"The Soviet Navy became interested in lightweight anti-submarine torpedoes in the mid-1950's partly through the need to improve coastal ASW capability in smaller ships, as well as providing a short-range anti-submarine weapon for nuclear submarines, leading to the development of 400 mm (40 cm) weapons which were generically designated Type 40.

The first, SET-40 or 40-61, entered service in 1961 with the "Poti" class corvettes (Project 204 Small Anti-submarine Ship).

Simultaneously they were issued to a variety of nuclear-powered submarines that had tubes (usually in the stern but, occasionally, in the bow). These weapons apparently entered service with the Project 658 ('Hotel' class) ballistic missile submarine K-19 in November 1960. The following year they entered service with fleet nuclear attack submarines of Project 659 ('Echo I' class), the first of which, K-59 and K-66, were commissioned in December 1961. Vessels equipped with Type 40 torpedoes included the 'Delta II/III', 'Hotel', 'Yankee', class SSBN's, 'Charlie' and 'Echo' I/II' class SSGN's as well as 'November' class SSN's.

These weapons were not issued to what the Soviet Navy classified as Large Anti-submarine Ships until the late 1960's and then only as helicopter-carried weapons. These first equipped the 'Krivak' class frigates.

Export versions of these torpedoes include the air-launched APSET-95 and UMGT-1ME as well as the surface-ship/submarine-launched USET-95 and Latush. An air-launched 350 mm weapon also exists with the export designation APR-3E."