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The Grebe was part of the Kingfisher family of guided anti-ship/anti-submarine weapons, which was developed under the prime contract of the National Bureau of Standards (NBS). Originally projected as Kingfisher E in 1946, it was subcontracted to Goodyear, and redesignated in September 1947 as SUM-2 (SUM-N-2 from early 1948) Grebe. Grebe was the only ship-launched missile in the Kingfisher family, the others (including the AUM-N-2 Petrel (Kingfisher C), AUM-N-4 Diver (Kingfisher D) and AUM-N-6 Puffin (Kingfisher F)) all being air-launched. The Kingfisher E specification in 1946 called for a subsonic rocket-boosted heavy MK 35 torpedo, which was to be launched from surface ships. By 1948, the payload had been changed to a lighter MK 41 torpedo, and a long-range version with a pulsejet sustainer propulsion was also planned. The SUM-N-2 was launched in the direction of a sonar-detected target, and after a preset distance, it began its terminal dive to release its homing torpedo. Grebe was mainly intended for use against deep-diving submarines. Twenty XSUM-N-2 prototypes were built, and flight-tested around 1950. Grebe never became operational, reportedly because none of the then existing sonars could match the missile's range. However, the date of termination of the SUM-N-2 program is unclear, because source [1] quotes both 1950 and 1953.  *Note: The "AA Target MK 52 MOD 2" label is a fake deception marking