The U.S. Navy has been talking about littoral warfare for years, yet no effective weapon system has been developed for use against diesel submarines in those confined waters. Water conditions in the littorals make acoustic prosecution by torpedoes extremely difficult. A bottomed submarine makes the problem even more tenuous. Some of the lessons learned from early antisubmarine warfare (ASW) tactics can be used today. In addition, there is an effective ordnance device that could be used against this continued threat: the cluster bomb unit (CBU).
During World War II, when acoustic localization was difficult, the Allies developed the Hedgehog weapon system. It delivered a large pattern of weapons in the water that greatly improved the probability of inflicting damage on submarines. The CBU has proved a formidable weapon in land-attack scenarios and it could be applied in the ASW role.
The CBU is a large weapon that releases dozens of submunitions (bomblets) on a target area. In some of these weapons, each bomblet detonates differently according to the surface it strikes. For example: a bomblet that hits armor plating or a hard surface such as an engine block will detonate as a shaped charge and can penetrate several inches of armor plating; if the bomblet hits the ground, it bounces in the air and detonates, throwing shrapnel that is effective against personnel, parked aircraft, and other targets.
An attack against a diesel submarine in shallow water does not need to destroy the submarine—it only needs to cause enough damage to make it easier for the current inventory of Navy torpedoes to attack and destroy it. Thus, relatively minor modifications would convert the CBU to an effective ASW weapon:
- The shaped-charge bomblet should be designed to ensure it maintains the correct orientation as it falls through the water. When it hits the sub's hull, it will punch a small hole. On a single-hull boat, this will result in minor flooding and additional internal damage from flying melted metal fragments. On a double-hull boat, flooding may not result, but holes in addition to the outer hull's limber (drainage) holes will increase the noise made by the sub.
- Bomblets that do not hit the hull would detonate at a preset depth. The combination of noise from the bomblets that miss the sub and the damage caused by those that hit it would cause most subs to take evasive action. The increased noise of an escaping submarine will make it an easier target for Navy torpedoes.
Conclusions
Numerous cluster bomb units delivered near an enemy diesel submarine in littoral waters could result in hits that set it up for the kill. Redesign and modification of available CBUs will be less expensive than developing a new system—and they could be put in active service quickly.
Captain Skinner, a submariner, is director of international plans and policy on the staff of the Commander, Pacific Fleet.