Part Two
Editor’s Note: 1he July 1998 issue of THE SUBMARINE REVIEW introduced the concept of using a novelist’s approach to the future, a la Jules Verne, to examine potential innovations to the technology and operation of America’s submarines. A time frame for that conjecture was chosen far enough in the future to avoid issue with current programs and developments, but not so far as to be beyond concern. Mr. Buff, a professional writer, has used all unclassified, public sources as the basis for his extrapolations of what-is to what-could-be.
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 a FSSN (defined as Future SSN in Part 1 of this article) in the littoral zone another 20 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.)
S. 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 leading 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 ladderequipped 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 regressing harbors, potentially reducing the security of operations by subs specially adapted in this manner.
Control Surfaces and Maneuvering Thrusters
A potentially useful design variation would be to alter an Xstern in 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 stem instead, with surfaces still 45 degrees off the horizontal like an X-stem, 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 surface 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 electricpowered pump jets, could be designed-in to provide both horizontal and vertical control at both bow and stem (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 Xor 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 stem at low speeds, since the box stem’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?
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 light-beam laser buoy. A variant on a couple of traditional ideas, gertrude (underwater telephone) and sofar (explosive charges signaling 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 themselves in encrypted form. Similarly, over tactical ranges, a carrier battlegroup 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.
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 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 tum 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 stream 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 can effect 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 seemingly never-ending 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 and 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 rendezeous 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 H202), 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 mihisubs. This is because oxygen, hydrogen, and hydrogen peroxide are all extremely hazardous materials. Pure oxygen systems are dangerous enough 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 a 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 of necessity will remain indispensable parts of the United States’ national defense. Acting as super stealthy mother ships for minis, and as the ideal milch cows for diesel or AIP boats, they’ll provide a force rapidly and irresistibly to dominate any shallow water area in the world. Purpose-built and ordnance-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 nature 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 in ending let us 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 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 .. pom the sea.”
APRIL 1990: INYENTOR-BUILDER JOHN P. HOLLAND DELIVERS FIRST U.S. SUBMARINE
John Merrill
