Do submarines have a future? They are the oldest stealthy vehicles. It is often argued (recently by the chief of naval operations himself) that accelerating computer power (Moore’s Law) is likely to erode anti-radar stealth for airplanes and, presumably, for surface ships. Can the end of submarines be far behind? After all, for years there have been claims that the seas would soon be rendered transparent.

During the Cold War, advocates of the mobile MX missile claimed that the Soviets were on the brink of doing exactly that, and therefore that their weapon should be bought instead of the expensive U.S. Navy Trident missile and the big submarine carrying it. Those claims collapsed. After the end of the Cold War, it became clear that the Soviets were nowhere near the point at which the oceans would become cloudy, let alone transparent. But many generations of computer chips have come and gone since then. Is the end nigh?

Obviously, efforts to detect submarines in exotic ways are highly classified – but that does not mean they work, or that they are likely to work. The sea is a far more complex medium than the air through which radar (to deal with stealthy airplanes and ships) passes.

Obviously, efforts to detect submarines in exotic ways are highly classified – but that does not mean they work, or that they are likely to work. The sea is a far more complex medium than the air through which radar (to deal with stealthy airplanes and ships) passes.

The more we know about the sea, the more a submarine commander can take advantage of its quirks. At least as important, it seems that it is difficult or impossible to sense remotely local details of the sea – such as the precise way in which temperature changes with depth – with enough precision.

Apparently you have to be in the sea to sense what is happening around you, and even then you cannot know what is happening nearby, where a submarine may be. We can probably reliably detect a submarine within a few miles – but that is very different from rapidly searching a wide area in which a submarine may be. And even that is a very expensive proposition available to very few countries.

There is concrete evidence that the submarine detection problem is far from solved, in the form of active building programs (including long-range plans) in many countries, including the United States and Russia. Those imagining that the submarine detection problem has been solved may argue that navies are unwilling to admit that a favored kind of warship is finished, or is about to die – in much the same way that it used to be said that “battleship admirals” prolonged the life of big-gun ships.

However, the reality of the battleship story is a lot less discreditable, and in many countries – certainly in the United States – there are powerful groups with vested interests in cutting spending, which means eliminating any kind of weapon system whose effectiveness can be denied. The U.S. Air Force’s attempt to kill Trident is a case in point. Precisely because of fear that the Navy was somehow concealing an uncomfortable reality, investigation of the supposed Soviet anti-submarine warfare (ASW) system was assigned to the CIA – which tried heroically to prove that there was some truth in the idea. It failed spectacularly. Nothing that emerged after the end of the Cold War changed that verdict. That is why the U.S. Navy continues to build nuclear submarines, and why nuclear ballistic missile submarines are assuming a more and more important role in U.S. national deterrence.

In fact, we see continued construction of large expensive nuclear submarines by all the countries that can afford them – the United States, Russia, the United Kingdom, France, and China, with India trying to join that club, and Brazil definitely interested. Meanwhile many countries, particularly in and around Asia, continue to buy non-nuclear submarines, in some cases equipped with air-independent power plants whose advocates claim that they offer a new kind of non-nuclear performance (and invisibility).

At the same time, the unit cost of submarines is high and growing, so the numbers in each fleet are declining. The U.S. Navy, for example, is building nuclear attack submarines at a rate that will support a stable fleet of about 30 to 40 – compared to 100 during the Cold War.

The Chinese People’s Liberation Army Navy (PLAN), which is certainly an enthusiastic submarine operator, has seen its numbers collapse after discarding a mass of submarines built to Russian designs of the 1950s. As in the West, the result is a much less numerous fleet of individually far more effective submarines.

To guess where all this is leading, think about what a submarine offers. Above all else, it offers stealth. For example, both a submarine and a satellite can collect signals intelligence. The victim is probably aware that the satellite is overhead (although considerable effort is spent concealing the identity of the signal-collecting birds).

What follows concentrates on the U.S. Navy, and to a lesser extent on the Royal Navy, and on missions beyond the classical one of attacking surface ships.

To guess where all this is leading, think about what a submarine offers. Above all else, it offers stealth. For example, both a submarine and a satellite can collect signals intelligence. The victim is probably aware that the satellite is overhead (although considerable effort is spent concealing the identity of the signal-collecting birds). He can turn off some critical transmitters; he can even deliberately emit misleading signals, because he has a good idea of what is being picked up. By way of contrast, a submarine offshore may well be invisible, at least to whomever is emitting. It may pick up only a fraction of what a satellite or airplane does – but it is far more likely to pick up what matters.

Moreover, sending overt intelligence collectors into an area inevitably raises tensions. A government interested in finding out what is happening without affecting events (until it wants to) has almost no alternative to a submarine.

Similarly, a submarine carrying land-attack weapons or special operations forces (SOF) can operate quietly within range of a target area. Unlike, say, a battle group, it does not affect events simply by being there. But it can certainly affect events if it acts. Against that, the submarine has far less capacity than the surface battle group. It may be most effective if it works to enhance the value of the battle group.

Intelligence-gathering, land attack (non-nuclear), and SOF insertion all have long histories in the submarine force, but with the end of the Cold War, they became far more important for the U.S. Navy and the Royal Navy. For example, both navies became interested in the way in which submarine-launched Tomahawks could clear the way for carrier air strikes. Because the submarine could fire from an unexpected direction, enemy air defenses likely would not be focused there, and the missiles would probably penetrate to their targets – such as enemy air defense control sites.

The question now is how to square such missions with declining numbers of increasingly expensive submarines. The two most important new factors are probably unmanned vehicles (both aerial and underwater) and improved communications.

Unmanned vehicles expand the footprint of the submarine. For example, several years ago EDO Corporation (now part of ITT Corporation) displayed a signals intelligence collection system adapted to an unmanned vehicle, which a submarine could launch from well offshore. A submarine might operate one such device in hopes of staying farther from an enemy’s anti-submarine defenses; but such defenses are slim to nonexistent throughout much of the Third World. It would probably be much more important that one submarine could operate several such devices at the same time, gaining much better and more continuous coverage of an enemy area. Each device would record signals, but it would take specialists aboard the submarine to make sense of them for onward transmission. Given improvements in underwater communication since the late 1990s, the submarine might also exert a degree of control over the unmanned intelligence collectors.

Intelligence collection in the Third World benefits from the fact that in many countries, nearly the entire national telephone system is based on cell phones – on radios. Some years ago, a U.S. presentation on future submarine systems included a mass launch of micro-UAVs (unmanned aerial vehicles) intended specifically to settle on (and exploit) cell phone antennas.

Intelligence collection in the Third World benefits from the fact that in many countries, nearly the entire national telephone system is based on cell phones – on radios. Some years ago, a U.S. presentation on future submarine systems included a mass launch of micro-UAVs (unmanned aerial vehicles) intended specifically to settle on (and exploit) cell phone antennas.

Another unmanned mission that a large submarine can support is mine reconnaissance. No one would send a submarine into a potential minefield in order to map it in advance of a surface force. However, the submarine can certainly launch an unmanned vehicle that can explore such an area. Several such vehicles can explore the area more quickly. Again, it takes operators and analysts aboard the submarine to make sense of what the vehicles find. They in turn can provide an approaching surface force with guidance as to where mines may and (probably more important) may not be. Mine reconnaissance or, better, automatic mine detection, might be envisaged as a kind of intelligence gathering.

Why use a submarine for the mission? Because mine clearance or even overt mine reconnaissance by surface ships tips off a potential enemy. It is conducted only if some follow-on force is likely to be operating in the possible minefield. That might be particularly critical if the area of interest was off a projected amphibious assault area. If a landing is a surprise, it has a good chance of success. But if the enemy knows what is coming, he can build up a force on the beach (or near the amphibious objective). No one today has enough surface mine countermeasures craft to clear multiple potential operating areas at the same time, so the sudden appearance of many such craft offshore is a definite tipoff. Moreover, mine clearance takes a long time, so if the enemy does not get the idea immediately, he has plenty of time to reconsider. On the other hand, the enemy usually has a limited supply of mines – he cannot lay them everywhere. Knowing where they may be laid allows us to appear somewhere else. We have already spent heavily to ensure that the Marines can cross extremely varied terrain en route from the sea to an objective, so an enemy can no longer limit his attentions to a few attractive beaches.

The unmanned vehicle(s) and the analysis on board the submarine are only part of the story; the data has to get back to the surface force. Submarines can employ high data-rate satellite communications, so relatively brief exposure of an antenna makes it possible to relay back what the submarine gathers of the offshore situation, including minefields. Even brief exposure is dangerous, but the farther out to sea the submarine can operate, the less likely that an enemy will be able to exploit it.

Submarines are the obvious means of inserting special operations forces (SOF), and for years considerable effort has gone into developing small submersibles they can ride to a beach (success has been mixed). The most interesting development, first tested about a decade ago, was the use of unmanned underwater vehicles (UUVs) to shuttle between a special operations team and a submarine acting as their command center. Again, anything that the submarine can deploy from a distance expands its footprint. In this case, the submarine was the converted ballistic missile submarine Florida (SSGN 728). A big UUV launched from one of its vertical missile tubes carried supplies to a team investigating a nominal weapons site. On its return trips, it carried soil for analysis aboard the submarine. The submarine, in turn, was far enough out to sea that it could transmit results of analysis back to shore, so that a decision could be made as to whether the SOF team should attack. Florida had been fitted with cruise missiles in place of her ballistic missiles, so in theory, the SOF unit would find targets for them. However, the most important part of the experiment was undoubtedly the support of the SOF unit.

Clearly, SOF can also be delivered by air, although it is not clear that they can be supported as easily once in place. What is clear is that the aircraft involved are sufficiently unusual as to be instantly recognizable.

Of course, there is also the anti-submarine mission so important to the U.S. Navy during the Cold War. Now it seems most often to involve diesel-electric submarines in relatively shallow water.

Anyone who follows aircraft blogs, moreover, will notice that unusual aircraft at overseas airfields are often quickly seen and reported – which might just ruin the element of surprise central to special operations. Covertness, the submarine’s key value, matters.

Of course, there is also the anti-submarine mission so important to the U.S. Navy during the Cold War. Now it seems most often to involve diesel-electric submarines in relatively shallow water.

For example, when NATO forces, including aircraft carriers, attacked the Serbians in Kosovo during the late 1990s, they had to contend with a Serbian navy that included small submarines. As it happened, the submarines never went to sea, but reportedly the U.S. Navy assigned several nuclear attack submarines to watch them.

What happens to this kind of mission if there are few nuclear attack submarines – perhaps too few to assign one to each exit from an enemy base? Can a nuclear attack submarine somehow split in two? Unmanned underwater vehicles may provide an answer. Some years ago, soon after a breakthrough in underwater communications, the Naval Undersea Warfare Center (NUWC) at Newport, R.I., proposed a new kind of vehicle, which it called Manta (after its unusual shape). Manta was to be an armed UUV with an underwater communications link back to the submarine. NUWC produced a film in which a future attack submarine closed off a port that had several entrances, stationing a Manta at each. The film was futuristic because no one had (or has) yet produced a suitable power source for the UUV. However, the idea that UUVs can deal with enemy submarines waiting to come out of their ports is certainly still extremely interesting. Perhaps, for example, they can penetrate unobserved, trail the enemy submarine out (or even fasten onto it), and then attack on command.

The reader should not imagine that UUV technology is so advanced that it is already widely deployed on board submarines. There are formidable obstacles. The UUV has to be able to navigate effectively, even though most of the time it is submerged and hence out of touch with GPS and other standard aids to navigation. It needs a power source good for lengthy operations – it may not be nearly as fast as, say, a torpedo, but it has to swim for much longer. It needs enough intelligence to overcome all sorts of underwater obstacles – unlike a UAV, it cannot be piloted on a real-time basis, because it cannot enjoy a continuous link back to the mother ship.

Where does all this lead? For one thing, if the role of the submarine is more and more to control and to exploit multiple UUVs (and perhaps also air vehicles), then the character of the submarine combat system changes. In the past, the combat system was designed to disentangle the underwater situation around the submarine so that its commander could recognize, hunt, and attack targets.

The problem of recovering a UUV underwater has apparently been solved. The U.S. Navy, which seems to be furthest advanced in developing naval UUVs, appears to be confident that the problems can be solved, and that within a decade or so UUVs will be a standard complement to submarines. It helps that UUVs are central to many of the modules being developed for the littoral combat ship (LCS), hence have a funding base extending beyond the submarine force.

Where does all this lead? For one thing, if the role of the submarine is more and more to control and to exploit multiple UUVs (and perhaps also air vehicles), then the character of the submarine combat system changes. In the past, the combat system was designed to disentangle the underwater situation around the submarine so that its commander could recognize, hunt, and attack targets. The submarine sonar room converted outputs of the various hull arrays into digital form so that, supported by its operators, the submarine’s computer could create a usable tactical picture. That tactical picture in turn could support an attack. The submarine’s other main sensors, its periscope and its electronic intelligence devices, were entirely separate from the sonar picture.

The underwater combat role certainly remains. However, often the system must concentrate on some very different task, such as interpreting the information gathered by a UUV. It follows that the computers and consoles on board the submarine may have to adjust to a widening variety of tasks. That is exactly what the U.S. Navy is doing in the Virginia class. The local area network (LAN) supporting the consoles in the command center connects not only to sonars and to the optronic periscope but, potentially, also to the output of UUVs. The consoles can reconfigure themselves easily for a wide variety of roles, supported by replaceable computers.

There is a second, subtler, issue. Compared to a surface ship of the same displacement, a submarine has perhaps a third of the usable volume. The new roles all demand more, not less, volume – for more combat system operators, for example, and for UUVs plus more torpedoes and missiles. Some of the weapons can be carried externally (as in the vertical Tomahawk tubes in U.S. submarines). However, the new roles do seem to demand a lot more internal volume.

Perhaps now is the time to revisit the idea – but in that case, we would have to accept poorer underwater performance, including poor maneuverability. Maybe the advent of lots of UUVs and SOF will make that a reasonable trade-off.

Submarine pressure hulls are cylinders, because that shape is best suited to withstanding water pressure (body-of-revolution hulls, which were pioneered by the submarine Albacore [AGSS 569], also have considerable hydrodynamic advantages). However, cylinders do not offer the most efficient use of internal space, because of the way they close in at top and bottom. A few years ago two submarine builders, Electric Boat in the United States and DCNS in France, pointed out that it might be more efficient to build a submarine out of multiple cylinders side by side. The idea is not new; for some years, the Dutch had triple-hulled submarines (in triangular arrangement), the Germans had figure-eight two-hull submarines, and the huge Soviet Typhoon submarines are built of mulitiple cylinders (the U.S. Navy sketched multiple-cylinder giant submarines in the early 1920s, too). The reason for adopting multiple cylinders varied, and only the Dutch seem to have done so to gain sufficient volume without building massive single cylinders. Perhaps now is the time to revisit the idea – but in that case, we would have to accept poorer underwater performance, including poor maneuverability. Maybe the advent of lots of UUVs and SOF will make that a reasonable trade-off.

This story was first published in Defense: Fall 2012 Edition.