During the 2018 Rim of the Pacific exercise, the USS Olympia (SSN-717) helped sink the ex-USS Racine (LST-1191) using a combination of Harpoon and torpedo shots. It was the first time in 20 years that a U.S. submarine was equipped with a submarine-launched anti-ship cruise missile (SLASCM).1 Though such exercises are not reflective of actual combat, the results stimulated interest in redeploying Harpoon on attack submarines. A submarine-launched Harpoon increases effective striking range, but will tube-launched SLASCMs put enemy ships out of action?
Excluding the three-boat Seawolf class, the SSN fleet consists of Los Angeles- and Virginia-class boats that can field a maximum salvo of four ASCMs from 21-inch tubes. Against small combatants, the probability of hits per ship has been estimated by some as only 32 percent, improving to 68 percent for targets that fail to defend themselves.2
A four-missile salvo, therefore, might be able to achieve one or two hits for well-aimed shots—potentially enough for a firepower kill of a small combatant. Larger ships likely will be more difficult to put out of action because of their greater staying power and better missile defense, so an initial salvo might accomplish little. If an initial strike precipitates an aggressive antisubmarine response, a successful first salvo is crucial. If one considers a more realistic salvo size of two (from a torpedo tube loadout of two Harpoons and two Advanced Capability torpedoes), a successful strike is less likely.
The stealthy nature of submarines makes them attractive ASCM platforms provided they can scout an opponent from long range and launch a sufficient number of missiles. The incompatibility of the Harpoon with the vertical launching system (VLS), however, limits maximum salvo size, a significant drawback. As retired Captain Wayne Hughes and Rear Admiral Robert Girrier noted in Fleet Tactics and Naval Operations, numerical superiority is the most advantageous variable in an exchange of salvos.3 Treating salvo size as proxy for force size, fielding a larger salvo improves the probability of putting an opposing unit out of action.
Currently, Kongsberg and Lockheed Martin are exploring VLS-capable versions of the Naval Strike Missile (NSM) and Long-Range Anti-Ship Missile (LRASM), respectively, including possible submarine-launched variants.4 Once they are available, the salvo size for the Los Angeles- and Virginia-class boats could increase to 12 (and more for Block V Virginias with the Virginia Payload Module). An ASCM-equipped Ohio-class guided-missile submarine with Tomahawk-like seven-shot/tube packing would provide a significantly larger salvo size, even with a mixed loadout. As future missile combat may involve saturation attacks, a submarine able to launch a large number of ASCMs will be better able to put capable opponents out of action.
Though models and historical data are imperfect predictors for future combat outcomes, against well-defended surface combatants a tube-launched SLASCM appears unlikely to achieve sufficient damage. VLS-compatible missiles offer increased salvo size, and a dedicated guided-missile submarine offers the best option for striking effectively first against better defended targets. Vertically launched SLASCMs should be considered as an option against smaller combatants, allowing more capable Aegis surface combatants and guided-missile submarines to focus on stronger surface units. When accounting for the manifold variables in an actual exchange, the maxim “more is better” remains paramount.5
1. Megan Eckstein, “VIDEO: Navy May Bring Back Harpoon Missiles on Attack Subs after Successful SINKEX; RIMPAC Also Highlights Ground-to-Ship Strike Capability,“ USNI News, 30 July 2018.
2. John C. Schulte, “An Analysis of the Historical Effectiveness of Anti-Ship Cruise Missiles in Littoral Warfare,” master’s thesis, U.S. Naval Postgraduate School: Monterey, CA, September 1994.
3. Wayne P. Hughes Jr. and Robert P. Girrier, Fleet Tactics and Naval Operations, 3rd ed. (Annapolis, MD: Naval Institute Press, 2018), 270–71.
4. See “Kongsberg’s NSM/JSM Anti-Ship & Strike Missile Attempts to Fit in Small F-35 Stealth Bay,” Defense Industry Daily, 18 December 2018; and “LRASM Missiles: Reaching for a Long-Range Punch,” Defense Industry Daily, 5 July 2019.
5. Michael J. Armstrong, “Effects of Lethality in Naval Combat Models,” Naval Research Logistics 51 (2004): 28–43.