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Looking Forward -- Nuclear Subs in 2050
by Joseph J. Buff, [IMAGE]2002

NOTE: [*] indicates reference to facts in the general open-source submarine literature.

Photo Courtesy: Walter P. Noonan
[IMAGE] Most members of the submarine community during World War Two could hardly have dreamed of nuclear propulsion, or titanium hulls, or supercomputer sonar signal processors. But apprentice torpedoman and squadron commander alike would have often yearned for the benefits such engineering marvels provide: longer submerged cruising endurance, greater test depths, and more powerful combat sensors. That was fifty years ago, and fifty years is a very long time, long enough to see both dramatic technological advances and major repositionings on the world geopolitical stage. What might naval submarines be like, and why may they be needed, if we project forward another fifty years?

This article will offer some suggestions and speculations, at once pragmatic and progressive, about the U.S. Navy's nuclear-powered submarines in the year 2050. Qualitative projections and suggestions will be offered as to future hardware capabilities, operational usage, and overall missions assigned, three factors that are always intimately related in naval submarine development and deployment.

Hull Materials and Test Depth
The continuing trend for many years has been toward greater test depth. Recent advances in materials science may lead eventually to improvements dramatically beyond today's roughly 1500 feet for steel (enough to stay below the Deep Scattering Layer) and 3000 feet for titanium (penetrating the upper reaches of the Deep Sound Channel).

Alumina ceramic composites, now being experimented with for research minisubs, combine tremendous strength with densities low enough to approach neutral buoyancy. Utilizing such materials to build a fleet submarine, one might obtain a hull that is extremely thick yet avoids excessive displacement, permitting SSNs and SSBNs to achieve an order of magnitude increase in operational depth without sacrificing useable internal volume or machinery and payload weight capacity. Let us begin to examine what such subs could achieve.

First, there would be two potential sources of enhanced quieting just from the hull design itself:

  • 1. A very thick hull may enhance acoustic isolation of the sub's internal machinery.
  • 2. The rigidity that comes with great thickness might prevent the hull popping sounds given off by conventional subs during rapid depth changes. (A thick and stiff hull might also avoid the need for internal ribbing, and might prevent hull resonances sometimes induced by internal machinery or external insonification, thus reducing active sonar cross section as well as passive signature.)

    In addition, cavitation of the propulsion system at high speed would be reduced, because the critical rotor RPM rate at which cavitation begins, everything else being equal, rises roughly with the square root of the depth [*]. This would raise top quiet speed, and might raise top maximum speed as well. That may become increasingly important in the future, not just for rapid transits to the battle area, but to achieve supremacy (water superiority?) once there against surface craft with ever higher flank speeds of their own. SWATHs, pump-jet driven freighters [*], ASW hydrofoils, and perhaps other propulsion breakthroughs hard for us to imagine, will all make it harder and harder for an attack sub to intercept an enemy carrier battle group or merchant convoy and do useful work against it.

    Within fifty years we may see both the need for and the available of funding to permit constructing what we might label an "FSSN," a Future SSN, or "FSSBN," a future SSBN. It is tempting to imagine a vessel able to routinely dive to, say, 15,000 feet, which is deeper than the average depth of all of the world's oceans. Here are some of the advantages for both offense and defense that such a capability would bring:

  • 1. Enhanced stealth, and thus survivability, relative to emerging ASW detection methods such as surface wake analysis, thermal plumes, magnetic anomalies, and blue-green laser scanning (lidar). (More sophisticated methods to reduce such signatures while at "shallow" depth can also be anticipated in the years to come.)
  • 2. Greater survivability through the thicker, stronger hull, which would be more resistant to enemy warheads both conventional and nuclear.
  • 3. Increased flexibility to play hide-and-seek below the Deep Scattering Layer, and within and even well below the Deep Sound Channel itself.
  • 4. "Nap-of-Seafloor" maneuvering over much of the ocean bottom. Submerged terrain such as seamounts, mid-ocean ridges, and trenches can form an ultimate battle ground with respect to a) stealthy approach toward an enemy coastline or operational area, b) concealment laterally from enemy active and passive sonar using intervening bottom contours, c) concealment vertically by hiding in sonar "ground clutter" or by lurking beside an old wreck, and d) ability to lie in ambush with "look up" sensors watching for enemy submarines and surface craft. In submarine warfare, there are real advantages to commanding the low ground. Additionally, the tactical need or desire to "stay off the skyline," while coping with bottom topography in close proximity to the boat, gives nap-of-seafloor combat some of the flavor of submarine littoral warfare.
  • 5. Availability of more horizontal seawater layers of varying density and reverberation characteristics, for enhanced concealment from enemy ASW forces and their weaponry. Deep ocean currents and marine life concentrations can create such layers well down in the bottom isothermal zone.
  • 6. Reduced effectiveness of conventional enemy torpedo and depth charge warheads with greatly increased depth. (Of course this would apply to one's own weapons directed against deep targets as well, suggesting the need for R&D on explosive charges and delivery platforms that would work well at pressures of three or four tons psi.)
  • 7. Reduced cavitation of high-power active sonars. The "critical wattage" at which the water outside the dome begins to boil is higher with greater depth. This obviously improves effectiveness of the system.
  • 8. Ability to exploit vertical temperature/density "sonar terrain and weather" features found around volcanic vents and black smokers as their super-hot exudations rise and then disperse. An inverted cone would result that, given apex temperatures of 500 or 800 degrees Fahrenheit, would have profound effects on sonar propagation.
  • 9. Avoidance of the noise resulting from long-wavelength surface waves [*], which can penetrate down to 1000 feet and impair passive target detection.
  • 10. Greater vertical separation, and hence greater passive (and also active) sonar signature transmission losses, relative to enemy ASW surface forces (or shallow-diving submarines) that may have localized the FSSN. Assuming spherical attenuation, ten times the depth implies one one-hundredth the received signal strength.

    Let us consider next some additional technological advances that may improve submarine quieting during the twenty-first century:

  • 1. Development of permanent or semi-permanent hull coatings (as opposed to continually discharging long-chain polymers from the nose of the vessel), to more effectively reduce water resistance and flow noise. This would benefit speed, quiet, and sonar sensitivity.
  • 2. Increasing use of hull coatings and/or "tile" coverings to reduce active and passive "sonar cross sections."
  • 3. Development of hull materials whose compressibility is equivalent to that of water, thus becoming almost transparent to sonar [*].

    [Joe Buff / JoeBuff.Com] We can probably expect the competition between more capable sonars and quieter subs to continue indefinitely. More sensitive hydrophones, more sophisticated array designs, faster computers with bigger memories, and new signal processing algorithms, will all make it harder to hide when a sub wants to hide. Clearly, greater test depth provides an important advantage. Also, it seems likely that continuing research into marine biology, geology, and oceanography will have ever greater importance to national defense, if and when the deep ocean becomes (perhaps tragically) a theater of warfare. And what better platform to develop such vital data quickly and covertly, than an FSSN which can easily traverse the area in question?

    Sensors
    Beyond sonar alluded to above, other new and emerging sensor capabilities may become important. Consider three related ways a submarine might literally visualize the sea around it while well below periscope depth:

  • 1. Active imaging through blue-green laser line scanners. Increasingly powerful lasers, charge-coupled intensifying detectors, and image enhancement algorithms, may permit a sub's CO and crew to "see" the ocean in their immediate vicinity. (Non-reflective coatings would be desirable to reduce one's own detectability by such lidar emitters carried by enemy submarines or enemy surveillance satellites, aircraft, or surface ships, including dipping lidar and lidarbuoys.)
  • 2. Passive imaging through electronic intensification of natural bioluminescence. Many marine species emit such electromagnetic energy, especially when disturbed by intruders or as a method of luring prey. Certain bacteria living near hot vents also emit weak bioluminescence [*]. The "natural lighting" in the ocean depths could have important military uses some day.
  • 3. As in 3., except, at relatively shallower depths like as 200 or 1000 feet, electronically amplifying and using for illumination whatever sunlight (or moonlight!) does manage to penetrate.

    Since light is rapidly attenuated in seawater due to suspended particulates, these methodologies would apply only over relatively short ranges. However, since the density of marine life attenuates with depth [*], there may be areas of the ocean where "visibility" is better than near the surface. Great technical challenges would have to be overcome to create sensors capable of operating under ambient pressures of dozens or hundreds of atmospheres. Perhaps by the year 2050 it will be possible to "look around" to a range of 1000 feet or 1000 yards (ten boat-lengths?), even more. What benefits might this bring?

  • 1. Greater ability to detect and stalk enemy submarines, in several ways:

  • a. Another submarine would in some sea conditions leave a trail of underwater bioluminescence that may persist long enough to be detected by electronic means. Analysis of this trail might yield data on course and speed as well.
  • b. Another submarine's passage might also leave a trail of damaged or shredded marine life, which could also be detected by active or passive visual means. This would be true of both conventional screw-propeller and pump-jet powered vessels.
  • c. Nap-of-seafloor maneuvering might stir up bottom sediments, again leaving a "spoor" which innovative tacticians might exploit.
  • d. Persisting wake vortices left by the passage of enemy subs might reveal themselves through lidar Doppler effects, in an analogy to how aircraft radar now detect wind shear.
  • e. At short ranges, using reflected light, a submarine might be able to directly observe by "visual" means another submarine, even when the latter fails to show up on passive (or even active) sonar because of intervening acoustic scattering and diffraction. Enemy submarines might also be detected passively by their obscuration or blocking of available light, which relates to the sonar "hole in the ocean" issue alluded to below.
  • 2. New means to detect, avoid, and clear submerged or floating mines, using lidar with variable intensity and beam width. An FSSN with such imaging equipment would be better prepared to map or penetrate enemy minefields, which might sometimes have a more obvious visual signature that either an active or passive acoustic one. Unmanned (or rather, Uninhabited [*]) Underwater Vehicles (UUVs), or even robotic grapnels attached to the parent sub, might then be used to disarm the mines or move them aside.
  • 3. Improved ability to detect and avoid deep-draft surface vessels. This is a significant hazard when a sub is operating shallow near a harbor or along coastal or mid-ocean shipping lanes.

    The limited range of light underwater is not entirely a disadvantage, since it enhances the security of active visual scanning by an FSSN operating in the face of the enemy. Sometimes, as hinted above, an additional detection means that is only operative over short ranges can still be a powerful complement to existing methodologies (especially when it possess better inherent directivity). For instance, an FSSN which localizes an enemy boomer through a sound transient may then be able to track down that target, by proceeding to the original datum to pick up and follow the trail of effects the target's passing had on the surrounding medium. Complex tactics could evolve, including the intentional creation of a false trail, with doubling back to lie in ambush against one's pursuer. Again, the basic characteristics of the ocean and its contents and boundaries become an important subject of measurement and analysis. Underwater "meteorology," with its attendant understanding and prediction of both acoustic and visual conditions in different places and at different times, will remain a relevant topic for the submarine community in the future.

    Next, speaking of the ambient noise environment of the sea, ambient sonar may eventually become a routine operating mode of acoustic surveillance [*]. This technique uses the constant background noise of the oceans, resulting from surface waves, passing ships, marine life, and other sources, to "illuminate" targets and terrain features that may be surrounding one's submarine. This is a hybrid of active and passive sonar: the listening submarine does not transmit, but it is listening for echoes off of targets rather than just their self-noise. Ambient sonar can also be though of as a version of bi-static sonar, in which one vessel pings and another listens for the echoes.

    The flip-side of ambient sonar is listening for "holes in the ocean," obstructions to ambient sound resulting from enemy submarines in the vicinity. More powerful and subtle sonar equipment would permit detection in this manner at greater ranges with a lower false alarm rate. A submarine might defeat this mode of detection by actively transmitting a "replica" of local sea noises in the direction of a suspected listening enemy.

    Other recent articles in this magazine [*,*] have discussed approaches to the man/machine interface that cope with the potential information explosion resulting from new and multiple types of sensor data. We can undoubtedly look forward to ever more sophisticated virtual reality and/or holographic visual presentation modes that integrate optical and acoustic information (including three dimensional target motion analysis situation displays). This would be vital in high-speed nap-of-seafloor maneuvering, to avoid impact with bottom terrain or entry into canyon cul-de-sacs that leave one cornered by enemy SSNs or their torpedoes. The old concept of "highway in the sea" helm displays [*] becomes relevant again. Accurate large scale (i.e., finely detailed) seafloor maps will become quite important too, as will high-precision submerged navigation systems, since crashing into a seamount can spoil your whole day, and a sub doing 60 knots (not impossible) advances 1000 feet every 10 seconds. On a more positive note, observe that deep diving subs, with proper maps and using acoustic and/or optical sensors, could obtain valuable pinpoint updates of their inertial navigation systems by referring to submerged terrain features for a kind of "orienteering." This would be especially relevant for a futuristic boomer, whose survivability after launching would certainly be enhanced by an ultra-strong hull capable of diving to great depth.

    Some of these thoughts suggest that submarine warfare may in the future become more dynamic, three-dimensional, and fast paced. This will probably require an evolution beyond the traditional "course log and bell book" approach to conning the ship. Eventually, a closely-knit team might work under direction of the commanding officer to make continual changes to course, speed, and depth, striving to maintain the initiative in a complex underwater ballet not entirely unlike engagements between fighter aircraft or fighters and bombers. Simulations and wargaming could be used to get a better handle on this issue.

    Control Surfaces and Maneuvering Thrusters
    A potentially useful design variation would be to alter an X-stern into a "box-stern," with a <> shape, where the control surfaces intersect at their edges instead of in the middle. X-sterns give greater maneuverability than the traditional +-shaped rudder and stern-planes arrangement, and also give some redundancy in case of a partial failure among the control surface actuating systems [*]. A box stern instead, with surfaces still 45 degrees off the horizontal like an X-stern, would form a cowling or enclosure around the screw propeller or jet orifice. This would reduce the sub's total emitted noise signature except from directly astern. Since the control surfaces now lie outside the propulsor's wash, instead of right in the middle of it, overall wake turbulence energy is more diffused.

    Another useful feature might be an expansion of the concept of auxiliary maneuvering thrusters now deployed at the bow of some subs for use near the dock. Thrusters, perhaps miniature electric-powered pump jets, could be designed-in to provide both horizontal and vertical control, at both bow and stern (where turning moments are greatest). These could supplement existing control surfaces and trim tank adjustments, enhancing maneuverability during underwater sub-on-sub dogfights or while cruising in the littoral zone, especially with respect to more reliable depth keeping in shallow waters. Such thrusters could also substitute for bow planes and X- or Y- or other type sterns when moving at dead slow speeds, or when main engines are stopped to drift stealthily with the current through a strait or along a beach. Furthermore, they might compensate for a possible loss of effectiveness of a box stern at low speeds, since the box stern's control surfaces, as mentioned above, would lie outside the immediate area of the propulsor wash. And with such thrusters in place, why not consider retractable bow planes? Like the sail, they produce a strong echo from some aspect angles and contribute to flow noise and wake turbulence. Bow planes in some submarines are now already designed to be rigged in, for surfacing under the polar ice cap [*]. Why not extend the concept further?

    Basic Physical Configuration
    Submarines have come a long way from the shark-shaped bows, anti-fouling cables, and "cigarette decks" of World War Two. It's possible their basic physical configuration will continue to evolve in the future.

    For openers, consider the idea of a retractable sail. A sail is in part a support for the periscope tube, and in part a platform from which to conn the ship, while on the surface, with adequate visibility and protection from waves and spray. But with non-hull-penetrating periscopes (NPP) delivering electronic images on a TV screen, there is no longer a need for a direct optical path from the periscope objective down into the control room. Furthermore, while submerged there is no need for that protruding platform used just to maneuver on the surface. Thus, the sail could be moved to a different part of the hull and be designed to retract downward into a "well" along the boat's centerline. (Of course, some current submarine designs have fairwater planes mounted on the sail, but those could be moved to the bow instead.) What benefits might this arrangement provide?

  • 1. Elimination of sloshing of seawater down into the control room when in heavy weather (which, admittedly, adds drama in old war movies, but can't be very good for equipment life or crew health and morale). On the other hand, though, there's something to be said for the CO and OOD being able to shout through an open hatch right down into the control room, and then slide down the ladder to assume their submerged battle stations in a split second when preparing to dive.
  • 2. Reduction of drag, of flow noise, and of wake extent and turbulence. The speed advantage of a retractable sail is probably minimal [*], but reduction of wake turbulence could be important to stealth, especially when near the surface.
  • 3. Improved operating capabilities when running shallow. In particular, a retractable sail could give an FSSN in the littoral zone another twenty feet or more of "headroom" in which to carry out its mission. (Of course, special steps would be needed to assure adequate separation between the periscope objective and the main hull while the periscope is in use, such as a longer mast made of high-strength materials.)
  • 4. Reduction of radar cross section when launching or retrieving rubber boats carrying SEALs, Marine landing parties, and other special operations forces. (See below for an idea on futuristic swimmer delivery vehicles.)
  • 5. Reduction of active (and ambient) sonar cross section. The sail stands out like a "billboard" when insonified from abeam, relative to the specular reflection from the rounded hull. At some disadvantageous aspects, such as when well separated horizontally from a surface craft one is approaching or fleeing, because of the angles involved the front or read edge of the sail can significantly increase a submarine's Doppler signature as well.

    The ideal physical arrangement of stations in the control room has been a subject of active study [*]. Crewmembers with varying responsibilities need to interact and communicate rapidly during tense combat situations. Having separate compartments for sonar, weapons, and communications might interfere with this free flow of information and impair "group situational awareness." This might be solved through a "duplex control room layout," with a ladder-equipped balcony or mezzanine level above a conventional "main level" control room. This exploits three-dimensional packing to improve instantaneous human interconnectivity. Instead of speaking over intercom circuits or walking from one compartment to another, team members could speak directly and be in direct line of sight.

    If diving depth is to increase substantially, then reducing the length of pipe runs that carry ambient high-pressure seawater becomes more critical than ever. This has been receiving special attention since SUBSAFE in the 1960s [*], and will surely continue to do so. It can probably be anticipated, as we enter more and more an age of advanced "designer materials," that substances will be developed to create cylindrical structures resistant to great pressure from the inside (i.e., pipes), as a necessary complement to building structures able to resist high pressure from the outside (i.e., hulls). Different "designer materials" might be optimized for these two different engineering challenges. (In fact, a material that's strong against compression but "gives" against tension would be ideal for deep diving torpedo warhead casings.)

    Additional use of conformal wet and dry hangars, fitting within the basic teardrop hull shape, can also be expected in future submarine design, as an alternative to add-on external hangars or retrofitted pseudo-streamlined bulges. (The suggestion of adapting the missile compartment of "retired" boomers for this purpose [*] is really the same idea.) This would reduce flow resistance, flow noise, wake turbulence, and active sonar cross section. There could be other advantages as well: a) the sub would be made more stable by removing substantial weight and water resistance from a point a relatively large distance from the longitudinal axis, b) equipment in a conformal hangar may be less exposed to damage by near misses from enemy fire, and c) add-on hangars and equipment containers tend to be highly conspicuous when in port and while egressing harbors, potentially reducing the security of operations by subs specially adapted in this manner.

    Connectivity
    The ability for a submerged submarine to communicate with other friendly forces and national command authorities, and preferably communicate in both directions, will undoubtedly remain an area of active research for some time to come. This maintenance of connectivity becomes more difficult as a sub dives deeper, and as ASW detection measures make it more dangerous to come back up to VLF or lidar depth or launch a delayed radio or tight-beam laser buoy. A variant on a couple of traditional ideas, gertrude (underwater telephone) and sofar (explosive charges signalling in the Deep Sound Channel) might be helpful. This hybrid idea is to communicate acoustically, two way, covertly and potentially over thousands of miles, by disguising messages in imitation of natural underwater sounds.

    Over long range, an SSBN might receive emergency action messages that imitate interocean whale dialogue but are in fact specifically designed packets of data, presumably itself in encrypted form. Similarly, over tactical ranges, a carrier battle group might give seaspace management orders to its accompanying attack subs, or issue updated targeting details to an advance-deployed SSGN for an SLCM launch, said communications being mistaken by any hostile third party for just a bunch of random shrimp clicks. Finally, a swimmer delivery vehicle might home-in after a mission on the boat that dropped it off by exchanging noises that sound to anyone listening like a baby dolphin and its mother calling each other. If such underwater connectivity were perfected, more range and flexibility would also result for the control of UUVs.

    [Joe Buff / JoeBuff.Com] Special signal processors would need to be developed, to encode information and conversation for transmission and then for reception pass ambient noise through waveform structure "filters" to see if any genuine messages are present. Presumably these messages would be packaged in (highly classified) prearranged formats as to frequency spectrum and pseudo-random time distribution, in order for this means of communication to be reliable as well as stealthy.

    Future Propulsion Plants
    Ever since the Turtle went to sea and to war in 1776, submarines have been limited by the capabilities of their propulsion plants [*]. One significant issue in future nuclear submarine design, which also impacts on tactical employment, is that of reactor cooling.

    Although they have disadvantages, liquid-metal-cooled fission reactors might have certain advantages over water cooled ones. Because liquid sodium is a much more efficient absorber and transmitter of heat, liquid metal reactors run at core temperatures substantially lower than those of water-cooled plants [*]. This could permit quieter cooling systems, and might also bring a nuclear sub closer to being able to hover or even sit on the bottom, at least for a brief period. It's conceivable that advanced materials might eventually be designed to safely carry waste heat away from the core, when operating at minimal output levels with a stationary boat, and deliver that heat to the outer hull of the reactor compartment. There, it would be removed from the submarine by natural convection into the surrounding sea, all without critical components of the reactor room overheating in the process. Since seawater gets colder with depth, leveling off at 39 degrees several thousand feet down, deeper operations would aid such hovering and bottoming tactics.

    Another quite futuristic concept that could have great utility for nuclear submarines is fusion power. A fusion reactor might have some real advantages over a fission reactor:

  • 1. In one promising type of design, the hydrogen fusion reaction takes place in a small frozen fuel pellet which is heated and compressed by powerful lasers. The main waste products of the fusion reaction are energetic neutrons, which deliver the heat output, and minute quantities of helium, which can readily be vented from the boat. If power to the firing lasers is cut, no further heat is generated. In contrast, due to radioactive decay of fission products, a uranium reactor continues to create significant heat even after having been scrammed. Thus a fusion reactor would be even safer to operate than current U.S. naval fission reactors.
  • 2. When the fusion boat is eventually retired, the amount of equipment with residual radiation may be comparable to that of a fission boat, but there is no waste "core" of potentially dangerous radioisotopes like in a uranium reactor, which leaves behind tons of long-half-life toxins like plutonium or cesium-137. Thus fusion plants are more ecologically friendly.
  • 3. Since a fusion plant generates no new heat once stopped, it would be much easier to design a sub capable of hovering or bottoming at will. This would obviously grant significant tactical advantages both in shallow seas and out in blue water.
  • 4. Since the heat from a fusion reactor radiates outward from a point source rather than occupying a physically extended core, fusion plants may be ideally suited to thermionic or thermoelectric (thermocouple) generation of electricity. That wattage could in turn be connected to advanced permanent-magnet (even superconductor) electric drive motors [*], maybe coupled directly to the main drive shaft. Such methods would be much quieter than existing power trains, with their steam turbines and reduction gears [*].
  • 5. Hydrogen is available in profusion by electrolysis of seawater, and some fusion reactor designs may not even require the separation of the deuterium and tritium "heavy" isotopes. This being the case, a fusion powered nuclear submarine could literally gather its own fuel while it cruises in the deep! (Uranium also could be extracted from the sea[*], but would then need specialized processing into fuel elements which would have to be introduced into the "hot" reactor core while underway.)
  • 6. Uranium reactors, when shut down, temporarily generate "fission poisons" that prevent restarting during a window between about one-half hour and ten or so hours later. Fusion reactors do not have this problem. Again, greater tactical flexibility is obtained.

    A design disadvantage of fusion reactors is the need for an electrical "boost" to start up the firing lasers. This might be accomplished via a ultra-high-specific-amperage battery. It can be expected that in the future batteries will be able to store more and more electricity with less and less of a weight and volume penalty. That being the case, one can also look forward to solving the "fission poison" problem just mentioned for a uranium boat, by running a fission-powered submarine on batteries until the reactor can be restarted. (This is another potential argument in favor of electric drive.)

    Now let's consider the other end of the propulsion plant. One aspect of terrain avoidance in high-speed nap of seafloor tactics, and of aggressive submarine maneuvering in general, is the need for strong backing power. This argues for a screw (or pump jet power turbine) with controllable and reversible pitch. This would create immediate reverse thrust without even needing to change the direction of the main drive shaft's rotation, let alone stop and then engage an auxiliary backing turbine. Eventually such pitch control machinery, like that now used on gas-turbine-powered surface craft [*], might be able to withstand the pressure near the ocean bottom. Such a boat would then be able to brake very quickly, and when also equipped with a full suite of auxiliary thrusters could negotiate some very tight clearances among navigation obstacles wherever found.

    The Nuclear Sub as Mother Ship
    Given the ongoing debate on the relative merits of nuclear power vice alternatives like diesel boats or air-independent-propulsion (AIP), it's useful to write down a "Fundamental Propulsion-Type Equation" as follows:

    FSSN + Battery-powered mini-combatants = Diesel/AIP + better speed, endurance, stealth & survivability

    By minicombatants we mean battery-powered combatant minisubs designed to be carried by and deployed from nuclear attack submarines or SSGNs equipped with conformal hangars. The equation has a simple meaning: the FSSN provides fast transit times with unlimited endurance plus infinite recharging and air/water capacity for the ultra-quiet minis. These minis can reach as far into the littoral zone as one might need to go, yet they can readily return to the mother ship out in deep water for a crew rotation, mutual updating of intelligence, and reloading of weapons. "Light" torpedoes, and smart mines, might be carried by the minis for use against small patrol craft or merchant shipping likely to be encountered near enemy coasts, stored until needed in a magazine in the parent boat. In fact, the hard-docking rendezvous should take place while submerged, for greater security and survivability. Ongoing high-intensity littoral domination is thereby facilitated. Underwater replenishing, anyone?

    Locally-based diesel and AIP boats might also benefit by support from an FSSN or adapted FSSBN, recreating the old idea of the milch cow, except again with underwater replenishment now possible from a much more survivable "cow." An electrically powered chemical plant in the nuclear sub can create an unlimited supply of oxygen, hydrogen, and hydrogen peroxide (which is H2O2), directly from seawater. Reserves of diesel fuel and other consumables could be carried as well. The present writer has some bias, though, toward the purely battery-powered minisubs. This is because oxygen, hydrogen, and hydrogen peroxide are all extremely hazardous materials. Pure oxygen systems are dangerous enough as it is [*], without the need to supply large quantities to Sterling cycle or fuel cell submarines. In addition, diesel and some AIP boats have noisy power plants, and basing them in forward areas near anticipated conflict zones can compromise security and invite a preemptive strike before they even put to sea. Of course, transfer of electricity from the mother ship to the batteries in the minisubs is tricky when surrounded by highly-conductive seawater, but waterproof and pressure-proof electrical couplings do not seem an impossibility.

    The future nuclear submarine would also act as a mother ship for future swimmer delivery vehicles (FSDVs). Recent development of robotic mechanical tuna, which actually move through the sea using the same swimming motions as the real fish do [*], suggests an SDV design that, like the secure gertrude suggested above, also hides in plain sight, disguised as part of the ambient ocean background. SDVs could be constructed as one-man vehicles that from the outside look and act (and sound) like sharks, dolphins, or smaller whales. The vehicle body would need to be large enough to accommodate the battery, operating controls and machinery, and the swimmer and personal gear. Presumably depth capabilities would be limited, as would endurance. Such "FSDVs," resembling species endemic to the operational theater at the relevant time of year, thus able to fool sensors and lookouts alike, could penetrate even the most secure enemy harbor installations, cable landing sites, or other high-value objectives.

    Conclusion
    This article has sought to trigger some additional useful thought about future nuclear submarine development, while also arguing that these expensive assets will of necessity remain an indispensable part of the United States' national defense. Acting as superstealthy mother ships for minis, and as the ideal milch cows for diesel or AIP boats, they'll provide a force to rapidly and irresistibly dominate any shallow-water area in the world. Purpose-built and ordinance-laden strike subs will support the land battle far beyond the beaches. Strategic missile boats optimized for hiding, and attack subs optimized to eliminate the opposition's vessels both surface and submerged, will eventually make the entire ocean and all its natural boundaries part of their domain. Using to their tactical advantage both bottom topography and every acoustic and visual characteristic of the underwater medium, SSBNs will form the ultimate survivable deterrent, and SSNs will protect more capably than ever those global sea lanes critical to any prolonged future cross-ocean military conflict. Aggressor, rogue, or terrorist attack submarines, no matter how propelled, will be intercepted and destroyed far from our home waters. Connectivity and covertness will be enhanced greatly, as oceanography and engineering work together to let naval submarines and special operations forces deploy and communicate at will, indistinguishable from the ambient background of the sea, and in the very face of the enemy.

    Since, at any point in the decades to come, there will certainly be other nations with the hard cash and the will to build, buy, or rent this sophisticated weaponry themselves, we neglect continued funding for research and construction at our peril.

    But let us in ending be optimistic. Some day we may have submarines that refuel and even re-victual right from the very waters around them, trolling or skeining for the abundant nutritious life-forms there to feed the courageous men (and maybe some day women?) of their crews. This would extend submerged endurance until the only limit still remaining is the power of human determination, giving ever deeper meaning to the phrase, "Forward.... from the sea."

    Originally published in two parts in the July 1998 and October 1998 issues of THE SUBMARINE REVIEW, a quarterly publicatication of the Naval Submarine League, PO Box 1146, Annandale, VA, 22003. Posted here with permission of the Naval Submarine League.

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