Times change, and methods of warfare change with them—often in cycles. The U.S. Navy has shifted its antisubmarine warfare (ASW) focus to the littorals and to the prevalent threat: the quiet diesel submarine. And rightly so. The majority of vessels in or on the high seas today are transiting merchant ships and the U.S. Navy.
The littoral combat ship (LCS) was envisioned to perform littoral surface, mine, and antisubmarine warfare, which would permit safe access to contested littoral areas through the use of modules that could be applied as part of a mission package. Some mission-package concepts are straightforward; others are more challenging. ASW is one of these. It has always been a difficult war-fighting problem. In the littorals, it only gets harder.
The speed requirement of the LCS made it very difficult to incorporate hull-mounted sonar, and therefore it was dropped. Thus, offboard sensors seem to be the only option. The MH-60R helicopter, with its active-dipping sonar, the advanced low-frequency sonar, is an effective littoral ASW sensor and weapon system and is the most capable module in the ASW mission package. However, several helicopters, even with their concomitant mobility and capability, do not constitute the persistent, available, and cost-effective approach to ASW that a conventional destroyer system offers. It may be time to step back and consider some previous efforts.
20th Century Sonar Methods
During the Cold War, the nation that performed the most littoral ASW against the most stressing threat was the Soviet Union. Its primary adversaries were the quiet U.S. Navy nuclear attack submarines. The Soviets relied on active sonar as the preferred method of detection in the littorals. They learned that dipping sonar
lowering a sonar transducer into the water from an ASW helicopter on fast platforms was very valuable. Employing two or three platforms in a system was the most tactically effective. The Soviets not only employed dipping sonar on helicopters, but also on the Grisha-class ASW corvettes.Soviet Hormone helicopters and the Grisha corvettes are reported to have used the same dipping sonar: the Soviet-made "Shelon," or NATO's "Elk Tail." The helicopters worked together using "leap-frog" tactics, with two dipping, two flying, etc. The Soviets constructed their two largest classes of ships and the Moskva- and the Kiev-class aircraft carriers—which carried no fixed-wing aircraft—around these dipping sonar ASW helicopters. They were convinced of their utility. In similar fashion, Grisha corvettes used their dipping sonar in sprint-and-drift tactics. One ship would drift, actively pinging with dipping sonar, while another raced ahead to a calculated position.
Because passive detection ranges are more extensive than active, U.S. submariners detected these dipping sonar operations and most frequently abandoned the area. Thus, the Soviets achieved a very real ASW "soft kill." However, when three dipping platforms worked together, one could unexpectedly appear, denying the submarine an easy exit route. Helicopters could achieve this more rapidly but had a limited endurance. This was not true of the Grisha corvettes.
These vessels could remain at sea for days and make things difficult. They also had a hull-mounted sonar for conducting methodical searches at patrol speeds. This was useful, because dipping sonar requires a motionless platform. Thus, the Grishas employed both sprint-and-drift dipping sonar and persistent patrol-speed bow-mounted sonar.
The Soviets employed these tactics and systems to good effect. The waters around Soviet ports are colder than those of many littoral environments, with no chaotic mixing of temperatures found in many tropical waters. But the wind, man-made noise, surface-bottom effects, and the seasonal variations common to all littoral areas are nevertheless present. Also, the threats they faced were similar, in a number of ways, to those the U.S. Navy faces today.
Don't Reinvent the Wheel
Now that the United States has adopted the primary ASW focus of the former Soviet Union, perhaps it's time we consider its proven approach. Done within the limits and capabilities of the LCS, a very capable littoral ASW capability could be created: a hybrid of the Soviet school and modern modular systems. An off-the-shelf capability could be assembled at relatively little cost and complexity that would combine lightweight, low-frequency active sonars in an aggressive system.
Such a capability could be developed as follows:
- Install an over-the side helicopter dipping sonar on a hoist;
- Incorporate one of the new lightweight, low-frequency variable-depth sonars (VDS) with its fast hoist system to provide a hull-like sonar capability; and, possibly,
- Incorporate a portable version of an existing over-the-side torpedo launcher.
These systems would be modular and would not negatively affect the ship's performance. They would also occupy a fraction of the space and weight allotted for modular warfare systems, and the sonars are obtainable off-the-shelf. Additionally, a small, rapidly deployable, omni-directional torpedo detection system may also be useful.
Such a capability would make the LCS an active ASW participant, breaking with the present practice of putting the offboard systems in harm's way while the ship stands off and directs the operation. It can be argued that standing off is not possible when it comes to littoral ASW. The approach advocated here would take advantage of the LCS's high speed for attack as well as defense.
How would this work
During active ASW clearance operations, an LCS operating in conjunction with its MH-60R helicopter or sister ships would sprint to a location, use the very capable water jet-propulsion systems to come to an abrupt stop, and perform a quick maneuver to throw off any wake-homing torpedoes. (However, very fast transits through mostly cleared areas dramatically reduce the likelihood of being attacked, period.) A torpedo-detection system could be quickly deployed, and if a threat is present, the LCS could maneuver and outrun it by heading in any direction. Such maneuvers take full advantage of these ships' unique capabilities. Few combatants of comparable size, anywhere in the world, can stop, accelerate, and turn like an LCS can. So why not use it for something other than retreatingSpeed, Agility, and Portability
If no torpedo is detected, the active-dipping sonar could be lowered within seconds. In difficult tropical littorals that often have multiple distinct thermal layers, the sonar could be lowered to various depths if required. After clearing that position, the ship could sprint to the next position in conjunction with its partner or partners, driving potential adversary submarines ahead and away from defended assets.
For missions that require a continuous patrol of a previously cleared area, one of the new lightweight towed variable depth sonars could be used, which produces a hull-like capability for searching in front of the ship. Such systems can be trailed at speeds as rapid as 23 knots. (It should be noted that at speeds approaching 30 knots, all sonars are severely degraded by water flow noise along the transducer; thus, LCS is not alone in being blind to ASW threats while transiting at high speeds.)
An over-the-side torpedo system would be required for such an approach. Waiting to launch a light airborne multipurpose system (LAMPS) is not the way to detect a submerged submarine. A somewhat more portable version of the current LAMPS MK-32 over-the-side torpedo system (currently employed on Aegis ships) could be used. Torpedoes could be launched, possibly aft, out of the stern door. The ship would be required to perform a quick maneuver to get into firing position
just the kind of thing at which littoral combat ships excel.A demonstration capability with an acceptable level of integration could be achieved rapidly and at a relatively low cost. The MH-60R dipping sonar is not the optimum sensor, but it represents a very credible capability that could be rapidly integrated. A lightweight off-the-shelf VDS system could be installed off the fantail in modular fashion, possibly in conjunction with the boat-launching system. A demonstration system would allow an evaluation of the capability and the tactics. Government labs or contractors could accomplish this using various systems.
At present, the LCS approach is to avoid torpedoes altogether by never getting in range of a submarine. The approach advocated here would expose the LCS to threats, such as ships equipped with Aegis combat systems. The LCS' speed and maneuverability arguably make it the most survivable ship in the U.S. Navy from submarine and torpedo attack. The small size, cost, and crew also argue for taking a higher combat risk than with the Aegis system. Why not take new advantage of the existing LCS capabilities for offense, not simply defense
Fight or flight Why not both