A swarm—eight high-speed, fully networked patrol craft similar to the Pegasus (PHM-1)-class hydrofoils—would give a battle or amphibious ready group commander in the littorals more flexibility, battlespace awareness, and firepower.
The carrier battle group is the pinnacle of U.S. power projection, dominating the battle space out to 300 nautical miles as it transits into theater. This unchallenged supremacy diminishes, however, as the carrier approaches the littorals. In the near future, and in several select locations today, the close-in threat may be so great that it places unacceptable restrictions on the battle group commander's freedom of action. The multitude of potential threats inhabiting the littorals requires a solution of multitudes. The use of Streetfighter or swarm tactics not only can reduce the risk significantly but also can maintain U.S. battle space dominance.
The threat in the littorals includes "contact identification, land-based air, land/sea-based cruise missile systems, small boat or plane kamikaze-style attacks, mines, submarines, and theater ballistic missile attack." The proliferation and integration of cheap weapons (diesel submarines, torpedoes, mines, and cruise missiles), cheap command-and-control assets (cellular phones, commercial radio direction finding, and computers), and a multitude of low-tech sensors (such as fishing vessels) combined with a familiarity with the local turf could tip the balance in favor of a Third World nation.
Today, two countries are of significant concern. Both Iran and North Korea, intelligence services predict, will employ low technology, but in large numbers. Iran has 186 patrol craft, of which 38 are capable of speeds exceeding 40 knots; it also employs armed jet skis. North Korea has 419 patrol craft, 198 of which are capable of speeds exceeding 35 knots. If these potential adversaries were able to co-ordinate a three-dimensional attack, they could overwhelm some engagement scenarios and attack a carrier battle group or amphibious ready group successfully.
In Somalia during Operation Restore Hope, U.S. intelligence severely underestimated the capabilities of the local warlords, which led to the mistaken belief that these seemingly rag-tag forces would not challenge the superior U.S. firepower. However, a primitive but well-coordinated command-and-control network, predictable Blackhawk employment patterns, and smoldering resentment of U.S. pressure and tactics came together against the U.S. Army. Mohamed Farah Aideed achieved a "CNN defeat" of U.S. forces. The Navy does not need to relearn this lesson in the littorals.
Streetfighter/swarm tactics have been proposed as a concept to support the requirements of the Navy after next and reduce the risk to naval forces. The swarm—eight high-speed, fully networked patrol craft—would offer a multitude of sensors and distributed firepower, allowing a regional commander-in-chief (CinC) to assign a carrier battle group or amphibious ready group to the littorals with confidence, knowing the risk is acceptable and that he has more flexibility to respond. These numerous sensors, combined with the platforms' ability to operate in the enemy's littoral backyard, would greatly aid contact identification, and the swarm's use of multiple redundant units means that the loss of a single unit would not cripple the combat potential of the force as a whole.
Use of the swarm will require a shift in how the Navy employs and fits out platforms. The units of the swarm will complement the ships of the battle and amphibious ready group, as well as each other, in space awareness, information, and firepower. Each individual unit, therefore, does not need the most sophisticated sonar, radar, or weapon system; it just needs systems that are good enough. For example, a lower cost weapon system using guns that have a 50% probability of kill would be inadequate protection for a carrier battle group. Three such gun systems, however, would provide an 87.5% probability of kill (traditional weapon systems have a design goal of 85%) and eight would provide a combined 99.8% probability of kill (if all units had an equal shot at the target).
Lower cost weapon systems provide the battle group commander the added flexibility of economy of force. They also offer more options for proportional response while maintaining assured destruction of a threat. Consequently, these weapon systems could give a CinC more choices as to how to show the flag.
Swarm sensors (radar and sonar) need not be over-the-horizon systems. The swarm will provide total area dominance by virtue of its large number of distributed sensors, and thus its systems need to be effective only over a shorter range. In addition to easing financial and maintenance constraints, this will simplify contact evaluation.
Littoral Dominance
Three functional areas will dominate swarm design considerations: underwater dominance, surface and air dominance, and mother ship configuration.
Underwater Dominance: The most complex sonar environment is shallow water, where the bottom begins to interact with the sound propagation path. Bottom type (rock, mud, sand, etc.), bottom slope (angle of the perpendicular to the beach), bottom cant (angle of the bottom parallel to the beach), salinity, bottom laminate (the layered composition of the bottom), temperature, and biologics bend, refract, reflect, or attenuate sound as it moves through the water. Each interaction with the bottom and surface distorts the perceived direction to the target. Consequently, long-range sonar search in shallow water is very complicated. The swarm can simplify this problem.
For years the U.S. Navy has used minesweepers in shallow water to detect small metal objects on the ocean floor. These ships use high-frequency active sonar that has a limited range, and because of this the sonar evaluates direct path active sonar propagation only, which eliminates the complexity of multiple path sonar environments. A swarm, similarly equipped with high-frequency forward-looking and side-scanning sonars, could negate the difficulties of long-range sonar searches. Multiple platforms with high-frequency sonar can accomplish rapid wide area clearing or sweeping. To maximize swarm sonar efficiency, these ships need to integrate sonar, navigation, and the bottom topography database. By combining information from these sources, onboard computers can calculate the ship spacing and search speeds to guarantee the detection of different size submarines (including bottomed submarines) or mines (see Figure 1). This network would allow the ships to be driven in autopilot to sanitize the search area quickly, and unmanned vehicles eventually might be able to fill this role.
Underwater littoral dominance also will require monitoring the sanitized area for intruders. In the future, such monitoring could be accomplished using the expeditionary underwater sensor system (EUSS), a mobile sound surveillance system (SOSUS). SOSUS is an integrated system of hydrophones located on the ocean floor that detect acoustic emissions from passing submarines. Once implanted, EUSS would monitor the flanks of the littoral area and any egress routes near the beach where a sub could gain access to the sanitized area. The mother ship would monitor the deep-water side of the sanitized area.
After the littoral has been cleared of underwater threats, the swarm would continue monitoring the surface and air environment. They would remain in the littoral as forward scouts for the battle group and amphibious ready group.
Surface and Air Dominance: In blue water, a carrier battle group can defend itself against most air and surface threats. In the littorals, however, the threat is one of multitude. Iran's and North Korea's armed high-speed small boats could overwhelm our surface combatants. A swarm of eight ships, deployed using the computer interface to maximize interlocking fields of fire, could handle this threat easily.
The fastest growing danger in the littorals is cruise missiles, which are becoming more sophisticated, cheaper, and more available. These missiles fly so close to the surface of the water and have such small radar cross-sections that they are difficult to detect until they are fairly close to their targets. Short-range, point defensive weapon systems are adept at stopping incoming cruise missiles, but they destroy them at such close ranges that the resulting missile fragments, which still travel at very high speeds, can cause significant damage to the defending ship. Clearly there is an advantage in engaging these missiles at greater distances.
The swarm computer rapidly would evaluate all incoming targets and determine which available weapon system—including those on the mother ship—would best engage the missile. Because radar coverage would be over-the-horizon into the littoral, missiles could be neutralized prior to becoming threats to the escorts, and earlier detection would give the battle group more time to align its weapon systems to engage any leakers. The swarm's capability to engage missiles at long range would provide a third layer to the traditional carrier battle group missile defense (swarm, escorts, point defense).
We would not have to equip the swarm with a kinetic-kill capability. Rather than obliterating a cruise missile, the weapons of the swarm would need only to damage its aerodynamics, to destroy its ability to reach the carrier or her screening ships. Instead of high mass bullets, therefore, a smaller conventional round could be used. In addition, a smaller caliber round would increase significantly the number of engagements a swarm could undertake before running out of ammunition. Programming the swarm's close-in weapon system computer to vary the rate of fire—slower rates of fire against less lethal targets—also would increase total possible engagements. Another consideration is to use miniaturization to add a timed explosive to the round. The explosion would increase the number of metal fragments the missile would have to fly through and thus increase the potential damage to its aerodynamics.
Mother Ship Configuration: Two modern ship classes would be excellent test platforms for the swarm—the Ticonderoga (CG-47)-class cruiser and the Australian Navy catamaran. The catamaran could carry the swarm underneath the main section of the ship between the hulls. This would allow easy access to the swarm prior to launch, and the swarm could be launched with the mother ship at cruising speed. The Ticonderoga could be modified with two outriggers to make it a trimaran. These outriggers would serve as docking stations for the swarm. The cruiser also would bring needed firepower and computing capacity. Both these ships would work well for the initial employment, but the second-generation mother ship should be designed from the bottom-up using either a catamaran or trimaran hull (similar to the British Triton trimaran).
Catamaran and trimaran hull designs are faster, more stable in high sea states, have similar internal volumes as single-hull ships, and are more fuel-efficient than conventional hull designs. In addition, a trimaran's outriggers add stand-off range to the center hull, where vital equipment (computers, propulsion, living spaces) would be located. This stand-off range would make the ship more resistant to damage from attack.
Swarm ships need to be small and high speed. The Pegasus (PHM-1)-class patrol boat would meet these initial needs. These craft have aluminum hulls, resulting in a low magnetic signature, which reduces their susceptibility to many types of mines. They are air transportable, adding extra flexibility. However, these boats would require some modification. They would need high-frequency forward-looking and side-scan sonar, the addition of a modified close-in weapon system, and a computer communications suite to integrate the systems. The computer system would integrate (1) ship's position, bottom topography, sonar detection capabilities, and contacts of interest to generate a search plan (boat speed and spacing); (2) sensors, threat database, weapons inventory, and ship's position to select the optimum weapons engagement, and (3) ship's auto pilot, ship's position, target trajectory, and close-in weapon system bullet ballistics to provide a fire control interlock. This interlock would warn ships that they are about to drive into a bullet drop zone or target debris fall zone. Finally, the computer would use target formation and trajectory to best position friendly ships for interlocking fields of fire to engage attacking enemy high-speed boats.
Criticisms
There are disadvantages to the swarm—some perceived, some real. One perceived disadvantage stems from the "carrier mentality," the belief that bigger is better. However, many feel that the Navy has placed too much emphasis on big ships, which are designed for blue-water engagements and thus are vulnerable to attack in the littorals. A high/low mix of ships is required to operate in all possible naval scenarios.
A second perceived disadvantage is that buying the swarm will cost the Navy the DD-21 because there are not sufficient resources for both. The swarm and DD-21 are not competing for the same job; they both support power projection from the sea. However, access to the littorals will be limited without the flexibility of the swarm.
A real constraint is that small vessels have limited endurance. This can be minimized by using hulls that are know to be more fuel efficient and by incorporating refueling with the mother ship as part of the swarm design. A second hurdle is that swarm software is hard to develop, but as this software will benefit all Navy weapon systems integration, it will be worth the cost.
The swarm is a practicable naval tactic today. A force of multitudes will allow the United States to dominate the littoral tomorrow and well into the future. By incorporating evolving technologies and complementary weapons, these small ships can be easily modified to maximize their networking and lethality. This reasonably cheap force multiplier should be developed today.
Commander Skinner is a student at the Naval War College. He recently completed his command tour as commanding officer of the USS Louisville (SSN-724).