text: Development SUBROC was one of several weapons recommended for implementation by Project Nobska, a 1956 summer study on submarine warfare. Development began in 1958, with the technical evaluation being completed in 1963. SUBROC reached Initial Operation Capability (IOC) aboard the attack submarine Permit in 1964. When SUBROC reached IOC, the US Navy's admiral in charge of weapons procurement stated that SUBROC was "…a more difficult technical problem than Polaris."
  Operation
  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.