SUBROC could be launched from a 21-inch submarine torpedo tube. After launch, the solid fuel rocket motor fired and SUBROC rose to the surface. The attitude then changed and SUBROC flew to its destination following a predetermined ballistic trajectory. At a predetermined time in the trajectory, the reentry vehicle (containing the warhead) separated from the solid fuel motor. The low kiloton
W55 nuclear depth bomb dropped into the water and sank rapidly to detonate near its target. A direct hit was not necessary. The W55 was in diameter, long, and weighed . Some sources suggest the W55 evolved from the experimental bomb tested in the
Hardtack I Olive nuclear test on July 22, 1958, which had a full two-stage yield estimated at 202 kilotons. Researcher Chuck Hansen claims based on his US nuclear program research that the W55 and
W58 warheads shared a common
primary or fission first stage named
Kinglet. SUBROC's tactical use was as an urgent-attack long-range weapon for time-urgent submarine targets that could not be attacked with any other weapon without betraying the position of the launching submarine by calling for an air-strike, or where the target was too distant to be attacked quickly with a torpedo launched from the submarine. The tactical rationale for SUBROC was similar to that for
ASROC or
Ikara. An added advantage was that SUBROC's approach to the target was not detectable by the target in time to take evasive action, although the warhead yield would appear to make evasive maneuvers unrealistic. However, SUBROC was less flexible in its use than Ikara or ASROC: since its only payload was a nuclear warhead, it could not be used to provide stand-off fire in a conventional (i.e., non-nuclear) engagement. SUBROC production ended in 1968. SUBROC was never used in combat, and all 285 W55 warheads were decommissioned in 1990 following the end of the
Cold War. Because the nuclear warhead was an integral part of the weapon, SUBROC could not be exported to other navies, and there is no evidence that any were supplied to other NATO allies under the well-established arrangements for supplying other dual-key nuclear weapons. In 1980 a planned successor, the
UUM-125 Sea Lance, was authorized. In 1982 the contract was awarded to
Boeing. The system and its
W89 warhead were cancelled in 1990 at the end of the Cold War. ==See also==