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Dr. Rosenblatt is a board-certified anesthesiologist in private practice and a member of The Naval Submarine League.

Recent technologic advances that have been made in air independent propulsion (AIP) for submarines have improved the operational performance of nonnuclear submarines and, in doing so, rekindled a long standing debate pertaining to the optimal means for submarine propulsion. The cessation of the Cold War and the change in submarine missions from strategic blue-water operations to an era oriented to combat in littoral regions has contributed to this acrimonious debate. The recent commissioning by Sweden of two submarines, specifically designed with an AIP auxiliary propulsion unit, has furthered this controversy. With numerous nations contemplating the acquisition of advanced submarines, built with AIP propulsion or capable of future retro-fitting, the optimal means of submarine propulsion no longer remains an academic question.

Numerous articles on this subject have been published in the marine engineering and naval science literature. The techno-logic attributes of AIP were recently discussed in a comprehensive review article published in Jane’s Defense ’96. Notwithstanding the engineering technicalities of AIP that remain to be resolved, several associated factors warrant further discussion. The introduction of this new technology will have a significant impact on submarine warfare and present a new challenge for the U.S. Navy.

With the launching of the first nuclear propelled submarines NAUTILUS, in 1954, the United States Submarine Force has benefited from nuclear power and throughout the ensuing years became committed to this means of underwater propulsion. Four decades of consecutive operation and numerous analyses has confirmed their dedication to the nuclear powered submarine. The reluctance by the submarine community to consider alternative means of propulsion is neither unexpected nor unwarranted.

Throughout the era of the Cold War, conventional diesel electric submarines played a minor role. Diesel electric submarines were able to conduct on rare occasions successful attacks on surface ships and submarines while engaged in naval training exercises. In contrast, the supremacy of the nuclear submarine, in one dramatic moment, was well documented during the Falkland’s War when the British established naval dominance by sinking the Argentine cruiser BELGRANO with torpedoes launched from the nuclear submarine HMS CONQUEROR. Overlooked by the general public, but not by naval analysts, was the fact that the German-built diesel electric submarines, SAN LUIS REY, operated by the Argentine Navy, nearly sank HMS ILLUSTRIOUS. Had the Argentine torpedo guidance system not malfunctioned, the loss of HMS ILLUSTRIOUS would have profoundly altered the tactical deployment of British forces. The Argentine submarine undertook its attack on the carrier despite the best efforts of the British at conducting an aggressive ASW defense.

Isolated vignettes from the Cold War and the Falkland’s conflict do not, by themselves, represent sufficient impetus for the U.S. Navy to adopt non-nuclear propulsion for its submarines. It does portend, however, that the future threat from submarines equipped with AIP will complicate future naval planning as the operational characteristics of these submarines are improved and as more of these naval vessels are introduced into service.

The issues raised by the introduction of AIP and enhanced operational characteristics of conventional submarines cannot be addressed by merely an engineering or operations research analysis. The impact, despite the newness of the technology, is profound and warrants a fundamental review of the historical origins of the modern submarine and its role in combat.

While numerous primordial attempts had been undertaken to develop submarine technology, the formative years occurred early in the 20’h century and were led by two highly competitive individuals: John Holland and Simon Lake. Both of these inventors made substantive contributions which gave rise to the modem submarine. Both men were fiercely nationalistic and they developed submarines as a means to counter British naval supremacy. John Holland even received financial backing from the Fenian Brotherhood, an association of Irish militants. This influence, and the historical context of the times, profoundly shaped the course of submarine development.

Although John Holland is credited as the father of the modem submarine, Simon Lake-his arch rival-was the better inventor. His early craft were superior in performance and design features. He configured his submersibles fur shallow water operations on the undersea floor and even equipped them with wheels for locomotion while submerging. He also incorporated the prototype of the modern lookout chamber into his submarines and the first snorkel. This unorthodox approach, nevertheless, was successful. He gave repeated demonstrations of his craft’s unique capabilities to travel along the bottom in shallow water. In an attempt to attain financial backing for his efforts from the U.S. Navy, he once displayed his craft’s prowess by penetrating the harbor at Hampton Roads, Virginia, located and moved mines laid for harbor defense, and then conducted mock attacks on naval ships within the port. Despite this successful performance and a 1000 mile voyage from Norfolk to New York, he was unsuccessful in his bid to secure governmental or commercial funding.

The established navies of the word, as well as the Fenian Brotherhood, were oriented to the strategic sea control and denial potential of the submarine. John Holland ultimately emerged as the winner of this competition despite the fact that his submarines were technologically inferior to Lake’s and required several decades of refinement before being truly operational. Both inventors did share one common trait: neither were successful businessmen, and they died equally destitute.

Since World War I, submarine designers have emphasized the strategic role of the submarine. The changing world environment, following the Cold War, has modified this requirement. A profound and dramatic change in the mission of submarines has come about with the orientation of naval combat to littoral warfare. The ability to conduct anti-surface and anti-submarine warfare is no longer the primary role for the modern submarine. Special operations, covert reconnaissance and mine warfare have assumed paramount importance in this new defense environment.

The ability to operate in shallow water, less than 300 feet, is now the key constraint. The very economies of scale realized by the progressive increase in size of ocean-going nuclear submarines has become a limiting factor and detriment to littoral underwater operations. It is evident that a larger submarine is less maneuverable and more easily detected in shallow water, despite contentions to the contrary, than its corresponding smaller counterpart. Furthermore, the design of the current modern submarine, whether nuclear or conventionally powered, is optimized for deep water and open-ocean operations.

The combined height of the sail atop the cylindrical hull results in a tall vertical displacement. By doing so, it increases the minimum depth at which the submarine can operate while submerged in a safe manner. This necessitates at least 40 to SO feet of water under the submarine’s keel for safe operation, while the sail itself must be submerged an additional 40 to 50 feet to preclude the submarine’s presence being subject to detection from the air by various means. It is thus apparent that the modern nuclear submarine, as presently configured, can operate safely on a routine basis in waters that exceed 120-140 feet in depth.

This factor precludes effective submarine operations in many vital littoral regions of the world. The choice of submarine propulsion, in reality, is a secondary consideration once the issue of submarine size and hull configuration are determined. There exists, no doubt, a minimum critical displacement below which nuclear power is neither feasible nor practical. The smallest nuclear powered attack submarine in service today is operated by the French Navy: their Rubis class nuclear submarine displaces 2700 tons submerged and has a length of 236 feet. In contrast, the type 206 submarine, produced by Germany in the early 1960s, displaces 460 tons and was designed for operations in the confined waters of the Baltic Sea. A far more specialized craft was produced by the German Navy in World War II. SEETUEFEL, a submersible equipped with tractor propulsion, displaced a mere 35 tons but carried two heavyweight torpedoes slung in external mounts alongside of the tracks. It could be adapted for special operations and discharge frogmen through an underwater lockout chamber. While it is speculative, a submarine of similar size and probable configuration was used by Soviet Special Forces to penetrate Swedish harbor defenses in the 1980s.

This supposition is based on the finding of underwater track marks found within Swedish territorial waters and by the size of the openings cut in the anti-submarine nets enclosing their naval base. A much smaller submarine or swimmer delivery vehicle would have neither sufficient range to accomplish the mission nor the power to drag along the bottom the three to four ton cement blocks that were used to anchor the anti-submarine nets. These findings suggest that the Soviet Navy built a specialized submarine with tractor propulsion and configured for operation in ultra shallow waters.

Current submarines, whether conventional or nuclear powered, are not intended for seafloor operations. The accidental grounding, in Swedish territorial waters, by the Soviet Whiskey class submarine S 363 in the approaches to the Karlskrona naval base substantiates this point. Although this incident proved to be a diplomatic embarrassment for the Soviet government, such an occurrence in wartime would have been catastrophic.

It is evident that the underwater range and endurance of specialized submersibles is quite limited due to the use of lead-acid batteries. The substitution of modern batteries (i.e., lithium polymer) augmented with an AIP unit would yield a marked improvement in speed and operational range. By today’s standards, such a propulsion plant would be more compact, yet have higher power ratings. The resulting improvement in performance should not be underestimated. Based on relative specific power densities, there could be nearly a ten-fold increase in range and a commensurate improvement in speed.

The flexibility inherent in the placement of advanced batteries and an AIP unit within a submarine would allow for a radical departure from the design of present submarines. Concurrent advances in materials science and production techniques allow submarine designers a unique opportunity to fabricate a bottom crawler submarine with tractor propulsion that little resembles its larger brethren. The result may look more like the advanced designs being proposed for the low observable airborne autonomous vehicle (AA V) than any submarine now in service. The few illustrations released to the public that show the shape of the Tier Ill (minus) AA V are startling: the Dark Star, the name given to the previously highly secret project, appears capable of operating in either an airborne or underwater environment.

Many of the contentions presented in recent articles in the defense of the current modern nuclear submarine would no longer be valid given the development of a compact submarine configured for littoral warfare that incorporates the advanced technologies now available to submarine designers. Such a unique underwater combatant would manifest excellent stealth characteristics, having minimal acoustic, optical and thermal signatures. The use of tractor propulsion and azimuth pod thruster units, the latter located amidships in pivotal mounts, would improve dramatically maneuverability in confined waters. The hybrid propulsion unit has the potential to provide sufficient energy for greater underwater speed and endurance; in particular, the performance characteristics could be improved further by the adoption of high efficiency electric motors. The corresponding technologic developments in computer science and electronic miniaturization would, in turn, reduce the critical minimum displacement of the submarine, its energy requirements and the size of the crew. The increased range, albeit still insufficient to transit the major oceans, could be addressed by either forward positioning of the craft or transportation to the theater of operations aboard commercial heavy sealift vessels. The small displacement of these submersibles makes this latter option highly attractive. In doing so, it negates the major attribute or nuclear power-its preeminent excellence at high speed, long distance transits.

The availability of such a vessel would augment the existing capabilities of the U.S. Navy and its nuclear powered Submarine Force in this era of littoral warfare. To date, submarine operations within the Persian Gulf have been limited and problematic. A shallow water submarine, designed with AIP and advanced technologies, would expand the role of the submarine community in this region of the world. Such a submarine could be used in a manner that precludes safe deployment of either a Los Angeles class submarine or the proposed NSSN. AIP represents a further evolutionary trend over the course of this century. While its full potential has yet to be ascertained, this technological advance must not be dismissed simply because of its newness. It will not replace nuclear power for submarines in the U.S. Navy; rather, it has the potential to complement existing capabilities. Failure to capitalize on this emergent technology and pursue an aggressive proactive approach can only result in malefic consequences. It should be noted that this new development has not been overlooked by foreign submarine designers. AJP, even without incorporation of other advanced technologies, has the potential to alter markedly the dynamics of undersea conflict as we have known it.

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