The introduction of nuclear power plants and the teardrop shaped hulls to US nuclear submarines in the late 1950s slightly overshadows one other important development in undersea warfare at that time. Sonar arrays on submarines became increasingly large. The size of an array is directly linked to the wavelengths they operate on. Larger arrays allow use of lower frequencies. And lower frequencies generally propagate further through water than higher frequencies. This, coupled with advances in passive sonar signal processing, extended the detection range against submarines from around 4000 yards to 50,000 or even sometimes 100,000 yards, or 25 to 50 nautical miles.
The increase in detection range called for an increase in weapons range. There was a limit to just how far a conventional torpedo might travel. Further, at long ranges, while a target might be detected, the precision of the plot was rather poor.
And so, like many other programs in the late 50s and early 60s, the answer was nuclear weapons. Where surface ships could use DASH to prosecute long range targets, submarines would have to use something that could be launched from a torpedo tube.
The answer was SUBROC, or Submarine Rocket, the UUM-44 underwater to underwater guided missile. Development began in 1958, and by 1965, it was deployed to the fleet. After being ejected from a torpedo tube, a solid rocket motor would drive it to the surface. The missile’s inertial navigation system would follow a precalculated ballistic trajectory. At the calculated time, the booster would be separated, and the warhead would continue to the impact point. There it would sink and then its W55 5 kiloton warhead would detonate.
Unlike ASROC, SUBROC never carried a torpedo payload. It was only available as a nuclear weapon. While training and testing rounds were fired, no actual nuclear testing of an operational warhead were ever conducted.
SUBROC was deployed until 1989, with the end of the Cold War. A proposed follow on weapon armed with a torpedo, Sea Lance, was cancelled due to technical issues, cost overruns, and the perceived reduction of the submarine threat after the collapse of the USSR. Today’s US Navy submarine force relies solely on the M48 torpedo for anti-submarine warfare.