THE ability of technology to alter the international balance of power was mentioned recently by no less a commentator than Nikita Khrushchev, who declared in a note to President Eisenhower that the "heyday of surface navy power is over. In the age of nuclear and rocket weapons . . . these once formidable warships are fit for nothing but courtesy visits, gun salutes and as targets for . . . rockets." Surface ships are, in fact, fit for these functions, and for a few more which submarines are still not ready to fill adequately. Yet it is true that the submarine is already playing a far more important role in sea power than it has in the past; and it is likely to become the dominant naval vessel in the future.

The principal reason for the submarine's rise to prominence is its sudden emergence as a device for strategic bombardment. This development is the result not of any new property of the submarine but of a combination of technological advances in other fields. One is the creation of relatively light nuclear warheads; the other is the over-all advance in the guidance and propulsion of long-range rockets--particularly the development of efficient solid fuel propellants having large thrusts. The marriage of a relatively simple, nuclear-armed missile to the most stealthy and hidden of naval craft has created a new threat to the world's populations--the ballistic missile submarine.

The submarine's new capability should not, however, blind one to its limitations, which recent developments such as nuclear power plants and new inertial navigation devices have not removed. If the submarine is to be considered as a major naval vessel rather than an auxiliary, then it must establish its ability to carry out a wide variety of military tasks. The variety of missions which a modern navy may be called on to perform is reflected in the multitude of vessel types it possesses. That submarines have relatively few types is an indication that they have not as yet taken over many naval roles, although there are signs of proliferation. Except for such boats as were available at the outbreak of hostilities, we fought World War II with one type of submarine--the 1,500-ton "fleet boat." Today, the nuclear equivalent of the fleet boat displaces about 3,000 tons, and from it has evolved an entirely new and much larger form--the ballistic missile or Polaris boat. There are reoccurring attempts to build a specialized (and small) anti-submarine submarine, one form of which is our SSK (submarine killer), displacing 765 tons.

Clearly, the submarine is not expected to develop the capabilities of all other naval vessels. But in each of its roles--present and potential--it faces the handicap of inadequate means of communication. The ability of surface ships to work in concert with each other and with aircraft, guided by excellent communications of great capacity, is not yet paralleled by equivalent sonic techniques fit for submarine use. Little has appeared to indicate that the coördination of submarine wolf-packs or of submarine-surface teams would be much easier today than was the case in World War II. And an underwater missile launcher is of no value if it cannot be reached with the order to fire. Submarines do not lend themselves easily to convoy duty, and it is hard to picture them as efficient in anti-aircraft operations.

One could be much more condescending toward the submarine, in view of its many limitations, were there any certainty that in an all-out war surface ships would remain alive long enough to carry out their functions. But since this is not the case, submarines may be asked to undertake tasks for which surface vessels are inherently better suited--except for their vulnerability.

Meanwhile, the submarine retains unequalled capabilities as an instrument of attrition and blockade. In forms of war where nuclear weapons cannot be used, its really overwhelming ability to destroy surface ships would be unmatched. The point has often been made that ocean commerce is the cement that binds the Western Alliance together. Even the greatest of sea powers cannot survive the steady attrition of its cargo carriers, let alone its military vessels. Here the advantage lies all with the Soviet Union, which has a vast superiority in numbers of submarines and is not itself dependent on surface shipping to sustain its alliances.

But submarines can blockade submarines as well as surface ships, and this is a tactic to which Russia is quite sensitive. Whether it would be feasible to blockade all of the European coast and all of the eastern shore of Asia is another matter. During World War II, our submarines sank about 22 Japanese submarines and two German U-boats as an incidental to their other duties. With much improved sonars and somewhat better weapons, and with submarines a major rather than a minor objective, the score could probably be more impressive. Once the location of a submarine is known rather precisely, it is quite vulnerable; the problem is to find it in the first place and then to assemble the forces to track and destroy it.

In addition to their role in anti-submarine warfare, submarines also make good mine layers; and they are suitable for all sorts of odd jobs such as rescue and scouting missions.

It is rather futile, however, to speculate on how the submarine will be used tactically in a war of unknown rules and in an era of rapidly changing technology. It may be more useful to discuss its essential properties and the nature of its environment as a means of assessing its probable future role.


The submarine's main defense continues to be its ability to submerge and thus hide from its enemies. This "cloak of invisibility" is its sole armor, for it is among the most vulnerable of ocean-going vessels. If its inner (or pressure) hull is breached, it has little chance of ever surfacing again.

The sea, however, is an excellent hiding place. The sonars of World War II destroyers, for example, could at best pick up a submerged submarine only a few thousand yards away. Because salt water is a conductor of electricity, electromagnetic radiations of virtually all wave lengths are, for all practical purposes, barred from effective use. In fact, visible light will penetrate about as far as any practical wave length; and even in the clearest water the range of light is but a few hundred feet. Sound, therefore, remains the primary means of sensing below the surface. Although there has been much progress since World War II in the application of sound as a method of detection, it has been accomplished with the aid of increasingly large and complex equipment. It would be optimistic to describe these advances as breakthroughs. The sea contains non-uniformities, such as temperature and salinity gradients; beneath these layers the submarine can hide, screened even from the sonars.

But though the submarine is hard to find, it has in the past been handicapped by a grave loss in performance when submerged. Until the closing days of World War II, a submerged boat could do no more than seven or eight knots. At that pace its underwater endurance was about an hour; at best, it could stay down about a day. The main difficulty was the inadequacy of the energy supply. When the diesel engines of a submarine are running they can exhaust the air inside the closed hull in a matter of seconds; this makes it impossible to use them or any air-consuming reaction to generate power when the submarine is submerged, except by the limited expedient of snorkeling. Energy had to be obtained when the boat was surfaced and stored in electric batteries for later use.[i] When driven below by enemy destroyers, submarine commanders would resort to every possible means to conserve energy, such as turning off motors in their refrigerating and ventilating systems, or even turning off lights. But eventually, a surface vessel that maintained contact with the submarine could slow it down and kill it.

The hard-pressed Germans, who depended most heavily on the submarine, developed some of the clearest thoughts regarding its design and use. Late in World War II, they exploited the existing means of propulsion to the utmost in their famous Type XXI design. These boats could do over 15 knots submerged, for about an hour. This was accomplished by doubling the amount of battery capacity and by streamlining the hull, stripping the deck of its bristling array of heavy and light guns. The Type XXI had a snorkel so that its diesels could operate with minimum exposure of the submarine to visual or radar sighting. Fortunately for the Allies, the war ended just as this submarine started its patrols.

The performance of the Type XXI was, of course, an improvement in degree, not in kind, though it was sufficiently remarkable to attract imitation by those powers which had enough strength left after the conflict to continue with a naval building program. The new models continued to be closely tied to the surface and were still grossly inferior to surface craft in endurance.

Such was the past. With the launching by the United States of the first nuclear-powered submarine, the Nautilus, an irreversible change occurred in naval warfare. It gave the submarine an advantage which the application of nuclear power to surface ships cannot redress. Although surface vessels will acquire tremendous benefits from the use of nuclear power, the unique ability of the reactor to produce heat without using oxygen is not one of them. But it is of vital importance to the submarine. The surface craft always had virtually unlimited endurance. Now that the submarine also can have unlimited endurance, the advantage shifts in its favor. For, while both employ the same sensing devices, the submarine retains its invisibility and its ability to locate the surface ship before that vessel is alerted. As far as visual means are concerned, the reasons are obvious. The periscope, which is from two to five inches in diameter near its top, and sticks out of water only five feet or so (or, on occasion, as little as a foot), is a much smaller object than a vessel and is hard to spot by eye or radar in rough water. As for sonar, submarines can be made quieter than surface vessels. For hydrodynamic reasons, a sonar dome itself gives off more noise the closer it is to the surface. Most important, the submarine can vary its depth, finding the optimum location for its sonar in the complicated and changing stratification of the ocean.

Nuclear energy has cured, or greatly alleviated, not one but two of the submarine's greatest weaknesses as compared to surface craft. Until now it not only has been limited by its energy supply but has also had the unenviable distinction of being the most inefficient load carrier that goes to sea. Its pressure hull, tanks, engines and various internal appurtenances weigh so much that it has carried a ridiculously small payload. Armed with chemical explosives, then, it could not be a serious threat to land targets, for it would exhaust its ammunition before it had made more than a small dent in a really large or "hardened" target. The purpose of the three-inch deck-mounted gun which most submarines formerly carried (a few have carried much heavier weapons to no good purpose) was to sink small, undefended vessels and thus spare the use of a valuable torpedo.

With all its limitations, the submarine of the past was deadly when it could attack shipping unobserved. Against large and technically competent surface forces, German U-boats almost stopped the Allies in two separate wars. In the war against Japan in the Pacific, our submarines operated against a navy which failed to produce a top-flight defense and as a result they bled the Japanese Empire to death. After the war, the Japanese Government gave as the basic cause of its defeat the loss of its merchant fleet. Even so, we lost more than 50 submarines in the Pacific in World War II, perhaps half to direct enemy action. The Allies, in breaking the back of the German submarine effort, sank some 700 U-boats.

Today nuclear energy has made the submarine infinitely more dangerous. The concentration of destructive power in a small warhead has entirely altered the hitherto small "carrying" capacity of the submarine. One submarine today can carry enough explosive power to devastate the entire coastline of a continent. A fleet of submarines, even crudely deployed, can ravage a great power in one salvo.

Thus at the same time that nuclear energy has made surface ships more vulnerable, it has made submarines more mobile, more flexible and more destructive. Their longer range now gives them an increased, and increasingly important, ability to enter waters denied to surface ships by superior air, submarine or even surface power (and, it may be added, by climate). At the moment, the United States Navy can choose to disregard enemy surface power as a factor, but there was a long period after Pearl Harbor when our submarines were the only American vessels able to operate in the reaches of the western Pacific controlled by the Japanese. As air-to-surface missiles of greater range and accuracy are developed, large areas of ocean adjacent to lands controlled by a strong enemy will be denied to our surface navy. Okinawa offered a foreboding example of what air power can do against surface fleets. And nuclear-armed, supersonic missiles homing on a target are much harder to knock down than the Japanese suicide planes of World War II.

Finally, the voyages of the Nautilus and the Skate under the Arctic icecap indicate that even this ocean, which gives the shortest routes between North America and Eurasia, is potentially open to the submarine for military purposes, for the supplying of bases, and perhaps for trade. More than 60 percent of the Soviet Union's maritime frontiers are in the Arctic. The Arctic routes which lead into the Bering Sea, however, present severe navigational problems. The waters north of the Bering Strait are shallow, in general less than 200 feet deep except for one small valley. To get under or leave the icecap on the Alaska side can be something of a feat.

From the point of view of the Western powers, the most disturbing fact of geography as it relates to the submarine is that every one of the major nations except Soviet Russia has the bulk of its urban population within 200 miles of tidewater. And where people are concentrated there also are the major industrial plants, the transport and communication centers, the research and development groups, and many of the military installations--in short, the vitals of the economy. Using 1950 population figures, we find that missiles of 150-mile range, fired from just outside the nearest unblockable tidewater, would cover 78 percent of the urban population of Europe and 55 percent of that in the United States, but only 13 percent of Russia's. However, a 1,200-mile missile could cover virtually all the urban centers in the Soviet Union if the launching areas were optimally deployed. In other words, while a 200-mile missile launched from submarines is a grave threat to Europe and this country, a longer range missile (but one well within the bounds of present technology) is needed to create a similar threat to the U.S.S.R. Since at any given stage of technological development higher accuracy can be achieved at shorter range, the advantage will remain to some extent with the Soviets.

This close relationship between range and accuracy is one reason why the intercontinental missile will not lessen the importance of the submarine as a missile carrier. In the future as in the past, the ability to hit a specific target accurately will confer a fundamental military advantage. But much more important may be the ability of the national economy to survive the first strike. Even if land-based launching sites can be simplified and partially concealed, they can be located by the enemy at leisure and longterm plans can be laid to neutralize them. The ability of the missile-launching submarine to escape detection provides better protection than the thickest concrete. And though land-based missiles can also be made mobile, they cannot achieve the flexibility of the submarine, which needs neither roads nor rails. Finally, the submarine combines high mobility with some degree of protection from the sea itself. Surrounded by water on every side, it is remarkably well shielded from any immediate effects of fall-out or from thermal and radiation effects of nuclear explosions.

A further consideration in assessing the value of the submarine as a missile launcher is that it is free from political limitations. No elaborate treaties are needed in order to place Polaris submarines on the high seas, and their use can remain within our own control without becoming elements of discord in the domestic politics of other nations.


One important property of the submarine has not yet been exploited--its capacity for speed. Potentially, the submarine can be made faster than surface craft which must use the displacement-type hull (as opposed to hydrofoil, which is currently impractical for large ships). A surface ship, operating between water and a much less dense medium, air, must throw up waves as it moves. At low speeds, this does not involve an important loss of energy; indeed, the lower skin friction of the surface ship as compared with a submarine of equal weight gives it less "drag." But as the speed rises, wave-making becomes a more important factor. The point at which a submarine begins to have less drag than a surface ship of the same size depends on the waterline length of the vessel. Our Guppy class submarines, which are about 300 feet long and displace approximately 2,000 tons, begin to use less power submerged than on the surface at about 18 knots. And as the speed of surface craft increases, wave-making eventually absorbs so much energy that, regardless of the bow shape used, the ships cannot practically be driven faster. Even for large ships in relatively quiet water this limit is reached at about 40 to 50 knots. But the oceans are not always quiet and, as storms raise waves higher, ships must slow down or suffer damage. Thus, the Queen Mary, which can do better than 30 knots, sometimes finds itself moving at 10 or 12 knots in the winter months. Destroyers are deprived of their top speed by wave action more often than larger ships; which is why an 18-knot submarine can frequently, under realistic conditions, outrun a 35-knot escort.

The top speed of an underwater vehicle is limited by a phenomenon called "cavitation." This is, by a crude analogy, something like the change from subsonic to supersonic flow for airplanes. Just as Mach number is a function of temperature and pressure, so the onset of cavitation is influenced by depth. The deeper the submarine, the faster it can go before cavitation starts to increase drag sharply. If its hull design is governed primarily by hydrodynamic considerations a submarine can approach 60 knots before cavitation becomes a serious drag problem. The submarine must be buried to a depth four or five times its diameter before it ceases to raise a surface wave, which means that in the case of a hull 40 feet in diameter, the keel would have to be close to 200 feet down before the engines could be "opened up" with full effect. Efficient propeller action may still be a problem at such depths, and the suppression of cavitation noise would also call for greater submergence.


If the development of this new technology means in fact that surface shipping can be wiped out in any prolonged war, the submarine's capability as a cargo carrier must be studied seriously. Of course, if the next war is a one-day exchange of megaton weapons leaving the world in chaos, the whole question of ocean commerce is irrelevant. But many American and Russian students of warfare consider it likely that wars will continue and that either they will be limited or there will nevertheless be sufficient survivors of a first blow to continue a classic battle of attrition. In either event a nation can win only by landing men and supplies on enemy soil. With regard to men and arms, Henry A. Kissinger estimates that "it would require the entire available United States airlift, including the civil reserve fleet, over 30 days to move one division from the United States to the Middle East, provided all transport units were in position when the crisis occurred and provided they were not required for any other mission--two most unlikely contingencies." He goes on to discuss the recently organized Pentomic divisions, which weigh about half as much as the standard division and therefore could be moved in roughly half the time. He concludes that "the minimum requirement would seem to be a capability for moving the combat element (5,000 short tons) of one new type division simultaneously. To move the combat element of one such division to the Middle East simultaneously would require 200 C-133S at a cost of $1.9 billion for procurement. To airlift the entire division within 10 days would require 272 C-133S at a cost of $2.6 billion."[ii]

Even with stockpiling, the United States is dependent on heavy imports of raw materials. If we could not keep bulk cargoes of oil, iron ore, manganese, copper, etc., coming in continually, we would not for long be able to send supplies out to our troops or allies abroad. Emergency phases of this job could perhaps be done by airplane, at enormous cost; but for the long pull sea-going vessels would be required. If we continue to depend on surface craft we are gambling on the ability of our merchant marine again to operate satisfactorily in wartime. If we lose--and we are betting against the trend of military technology--there seems to be only one recourse: we must develop submarine cargo carriers.

The reasons for turning to the submarine as a cargo carrier are those of necessity rather than convenience--except, perhaps, in the case of liquid cargoes. As far as dry cargo is concerned, the submarine is inherently hard to load and unload, and, compared with surface ships, is apt to remain so. Ships can have hatches large enough to pass in a herd of elephants if necessary. Although these hatches must be reasonably watertight, they need not have the absolute integrity required of submarine hatches, which are traditionally small and few in number. And designers and engineers have long since learned that submariners are distrustful of any added or enlarged openings into the pressure hull. Surface cargo carriers can be festooned with booms, masts, winches and other paraphernalia for the rapid movement of cargo through the hatches and onto the pier. A submarine, which must be as clean of surface excrescences as a fish if it is to go fast and silently when submerged, must do without such aids, or it must painfully retract them when it submerges. Troops, however, are one form of dry cargo which are self-loading and unloading.

Despite all its inefficiencies as a cargo carrier, the submarine nevertheless can easily prove superior to a plane. During World War I, the U-boat Deutschland successfully made a round trip from Germany to the United States and return. Outgoing, it carried dyestuffs reputedly worth twice the construction cost of the submarine. It returned with a cargo of rubber and nickel. Today, a much more practical underwater carrier could be designed. Even so, the submarine will never be an economical way to transport dry cargo in bulk.

However, the submarine is more adaptable to the hauling of liquid cargoes. This primarily means oil, which makes up about half the tonnage moved across the oceans. Liquids can be carried in relatively light exterior tanks fully exposed to water pressure and they do not need the elaborate handling gear of dry cargo. Oil may also be carried in a flexible, self-supporting container, towed by the submarine.

Preliminary efforts to design a cargo submarine are under way in Japan, Britain and the United States, either with private financing or government support. Although the studies are far from completion, engineering information is nevertheless being amassed. As conceived on paper, the cargo submarines range from 30,000 tons at 23 knots to an enthusiastic 80,000 tons at 50 or 60 knots, the latter to supply England with iron ore from the Hudson Bay area or oil from the Middle East. Such specifications are undoubtedly feasible technically. Nor is there much doubt that the submarine can, far more advantageously than a surface ship, translate the unlimited power of the nuclear reactor into speed. But peacetime economics are heavily against the submerged carrier.

In summary, trends in technology are favorable to the submarine as against the surface ship. In spite of the increasing--and to some degree productive--research being devoted to the problem of detecting submerged submarines, these retain essentially all their past invisibility. Nuclear weapons and improved performance have given the submarine a new strategic mission and should enhance its traditional roles in naval warfare. The surface ship, menaced by both air and undersea power, may have to forfeit many of its functions to the submarine; the extent of the shift will depend largely on the degree to which the submarine solves some of its own problems, particularly that of communications.

[i] It is an interesting fact of modern technology that no very good means of storing energy is presently known. In terms of weight per unit of energy, batteries are not significantly worse than any other practical means. The hydrogen-peroxide submarine, which stores oxygen in a compact, chemically combined form, claims better performance than is achieved from batteries. Whether the improvement is worth the added risks and complications is a moot point.

[ii] "Nuclear Weapons and Foreign Policy." New York: Harper, 1957, p. 163 and 164.

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  • PAUL COHEN, Engineering Section Head for Anti-Submarine Warfare, the Sperry Gyroscope Company; formerly an instructor at Massachusetts Institute of Technology
  • More By Paul Cohen