A Quiet Revolution

target must be determined by a process similar to trian­gulation, but complicated by the target’s motion. The at­tacking vessel must change her position to develop a base line for the triangulation. This own ship’s motion cannot be too slow, or the base-line will be too short and the target motion complication too large. Nor can it be too fast lest the detecting ship’s own noise drown out the target’s signal. Furthermore, a course change by the target may distort the solution. If the course change is not detected, an erroneous solution for all parameters will result. Even if the course change (a zig) is detected, the tracking ship must then start the triangulation process again. Finally, the assumptions made to permit a passive fire control solution do not hold when the range to the target is short. Thus, when the rapidly changing tactical picture most requires clear and unambiguous information, the passive tech­niques fail.

These and other problems limit the range at which a passive sonar solution can be generated, both for long and short ranges. They severely limit the quality of such a solution. Only the use of high-speed homing torpedoes or nuclear warheads permit one to consider attacking sub­merged submarines with “bearings only” solutions. New initiatives may help, but even so, once an adequate fire control solution has been developed, the target has fre­quently closed to an uncomfortably short range. At this range, most of the advantages of our ASW weapons are nullified by the need to prevent the weapon from attacking or damaging the launching ship.

Given the great disparity in numbers between our sub­marine force and the Soviets’, we can ill afford to engage at short range where the rapidly changing geometry results in a confused tactical picture. In such an encounter, luck and the skill of the commanding officer and crew are far more important in deciding the outcome than sensor, weapon, or propulsion technology. We cannot expect a monopoly on any of these, but something we can expect if we are forced to engage at close ranges is large attrition rates.

Analysis: We now return to the question of the effect of the quiet revolution on the attack submarine ASW mis­sion. Any future opposing submarine force will be quieter. The physical laws of signal to noise lead inevitably to decreasing detection ranges. The value of a submarine in ASW decreases with the decreasing detection ranges, not only because of the decreasing volume of ocean that she can search, but because engagements at short ranges de­pend more upon luck and skill than high technology. We simply cannot afford to engage in the short-range attack lottery when the cost of a ticket, the price of a single submarine, is almost one billion dollars. We already have far fewer submarines than our expected adversary, and if our sensors cannot provide ASW submarines with a signif­icant tactical advantage, then the force cannot succeed in its mission.

The conclusion that the submarines we are building today may not be able to fulfill the ASW mission of the future is unpalatable. It did not please me when I first argued myself into this comer. In such cases, it is impor­tant to explore the tacit assumptions embedded in the argu­ment. It is assumed that the primary sensor will remain acoustic, in particular passive sonar; perhaps the innova­tive use of active sonar or nonacoustic sensors might change the picture. The tactical assumption is made that we will be outnumbered or that our submarines will be so few and so expensive that we cannot afford large attrition rates. Might there not be some way to increase the num­bers of subs and decrease their vulnerability to damage? Finally, there is the engineering judgment that there are few processing tricks remaining that might lower the threshold signal-to-noise ratio for detection faster than the rate at which the world’s submarines get quieter.

►  Primary sensors will remain acoustic. Although a sub­marine might emit many signatures, only one propagates to long ranges through the water: acoustic waves.² An unpredicted technological breakthrough might possibly occur in sensors, but planning on an improbable event is not safe. Moreover, it is unreasonable to expect that a new technology will remain our exclusive property. A long- range sensor available to both sides would unlikely im­prove our kill ratios; in fact, it would be a decisive disad­vantage to our outnumbered force. Finally, surface ships and air ASW forces could probably use the new sensor. This would eliminate the only advantage that submarines have over surface ships: stealth.

The likelihood of developing effective nonacoustic sen­sors has been the subject of top-level inquiry for some time. The question relates to the survivability of the strate­gic deterrent missile submarines. Little can be said pub­licly on this subject for “anyone who finds a way to gain an advantage in . . . sensor technology is usually a fool to talk about it, so that no public forecast of such advantage is likely to have much value: those knowledgeable enough to make reliable forecasts will not publish them.”³ The recent debate on the strategic package, however, is elo­quent in what it does not say about such developments. Had it been probable that any long-range sensor could be developed that might threaten the Trident submarine within her expected service life, the question of her sur­vivability would be hotly debated in Congress. It is not.

►  Caution: Active sonar can be hazardous to your subma­rine. If sonar is to remain king, must we be limited to passive sonar? For the most part, yes. Active search pro­vides an increase in risk to the tracking submarine without a concomitant gain. Active sonar is equally subject to the laws of signal to noise but with serious additional limita­tions. Most significant, the range at which a target can detect the active transmitter is well over twice that at which the transmitting sonar can detect an echo from the target. In the case of submarine-based ASW, inasmuch as the sonars are fixed within the vessel, the detectability of an active transmission makes the rest of the ship vulnera­ble. The submarine hull, which is already resisting ex­treme sea pressure, is not well-suited for absorbing damage. Thus, while there is still any chance that surprise may be achieved, U. S. submarines will do well to avoid using active sonar. We would be putting our subs at risk from an enemy’s long-range ASW weapons well before we could detect the enemy and launch our weapons.

Although it is possible to envision several forms of ‘covert” active sonar, I do not hold much hope for their successful development. They would be susceptible to countermeasures and could be seriously degraded by enemy efforts to reduce echo strength of their submarines. Perhaps the active transmitter could be separated from the ASW submarine to protect her from attack on the active sonar source. Such a system, however, would not resem­ble the submarines currently in production.

^ Numbers and attrition rates. One-on-one engagements at short range are examples of almost pure Lanchester lin­ear “law” combat. F. W. Lanchester showed in 1916 that the ability to inflict casualties on an enemy’s forces is proportional to the firepower of the individual unit and the numbers of units available.⁴ Were both sides given long- range sensors and the ability to direct fire at multiple units, the situation for the force with the numerical inferiority becomes even worse—the fighting strength varies as the square of the numbers of units engaged. We are already outnumbered three to one by Soviet attack and cruise mis­sile submarines, and, even though they probably possess mferior torpedoes, they maintain the edge in rate of fire. At short range, the superiority of our torpedoes may not count for much. We are left with a dilemma. If short-range detection is the rule, then submarine-based ASW is not tenable; if long-range detection is available to both, sub­marine-based ASW is even less tenable for the outnum­^bered force.

To gain numbers, we must reduce submarine acquisi- *°n costs. The most drastic cost reduction available to a ^su.bmarine designer is to replace the nuclear power plant ^wUh a non-nuclear one. My best estimate of the effect of ^SUch a replacement is a decrease by a factor of four in Procurement costs,⁵ although this is considered optimistic . y orany. Further cost reductions can result from decreas- ^lng the quality and quantity of manpower needed. How­ever, even if we stopped building nuclear submarines alto­gether, we probably would not achieve parity in numbers with the Soviets, given the current economic realities. What we would give up in force flexibility by doing so would be substantial. Although I believe, as do the Sovi­ets, that there is great value in building a mixture of nu­clear and non-nuclear submarines and although this would help alleviate some of the submarine-based ASW problem generated by the quiet revolution, this is not near a com­plete solution. The number of adversaries and the sheer volume of ocean needed to be searched are too great.

Some actions can be taken to ease the rate of fire prob­lem and to decrease the vulnerability of a submarine to weapon effects, but these are similar to the stopgap efforts available to improve the threshold signal-to-noise ratio for submarine detection. They are useful, valuable efforts, but they do not face the central issue. Moreover, submarines pay dearly to achieve the advantage of stealth they have over other vessels. Some of the tradeoffs required simply to have a submersible platform limit the resistance of the hull to damage, the number and size of the penetrations that can be made in the hull to provide high rates of fire, and the physical capacity to carry a large weapons load. Improvements in these areas are possible, but they are not independent of each other. Decreasing the vulnerability, for example, will increase the sub’s displacement, further limiting the weight of the weapons load. Such variations on current designs would be on the margin and inadequate to overcome our disadvantage in numbers.

► Signal or Noise? A final pillar of my argument is the assertion that the opposition is becoming quieter faster than we will be able to improve our detection capabilities. Quieting techniques already known to us are more likely in Soviet submarines than new clever detection tricks in ours or theirs. This is clearly a central issue and I cannot here make such a strong argument as I did for the primacy of acoustic sensors. I will, however, render without sup­port my engineering judgment as an experimental physi­cist and a naval officer qualified for command of subma­rines, and as one who is fully aware of the data processing explosion now taking place, that the assertion has a very high likelihood of being true. Moreover, regardless of the probability, the consequences of its truth are so grave that the issue should be given serious attention.

Where Do We Go from Here? Given the short passive detection ranges expected in the future, the vulnerability of active sonar platforms, and the increasing expense for hull and propulsion systems, one day we will find our­selves unable to support the ASW mission with subma­rines as we now know them. We must plan for changes in the nature of the submarine as a weapon system or plan to get it out of the ASW business. Because of the long lead times required for producing new nuclear submarines and the 30- to 40-year lifetime foreseen for such ships, it is important to consider now what will be needed in the next decades.

In the short term, we must continue as we are: attacking each perceived problem in isolation. But we should be aware of the quiet revolution as a general phenomenon and continually ask ourselves what we can do when much of the opposing submarine force is as quiet as most of our current submarines. Improvements in short-range tactics should help reduce the attrition expected in fast-paced sin­gle-ship engagements, but luck will still play a major part. Regardless of what role we plan for our future submarine force, we would be well advised to practice fighting at close ranges and to emphasize deployment of effective static passive ranging technologies that we have neglected for 20 years.

It does not take a whole fleet of quiet nuclear or diesel submarines to disrupt our plans for submarine-based ASW. It takes only a few such vessels to penetrate our too-widely-spaced barriers and ravage our surface supply or strike task forces. The Soviets need only match our 1966 technology, which built the Sturgeon (SSN-637)- class nuclear attack submarine, to do this. The threat of the quiet Soviet submarine is already with us; what we face in the future is an entire force composed of such ships.

What is needed to combat that threat is a large number of sensors, a smaller number of weapons delivery systems that can reliably communicate with the sensors, and plat­forms that are relatively invulnerable to submarine coun­terattack. Alternatively, the platform could be cheap enough that the destruction of a few will not cause a loss equal to our annual platform production. As a submariner, I am loath to admit that this sounds more like a prescrip­tion for an aircraft than for a submarine. Certainly, a simi­lar analysis of the air-based ASW system will identify problems, for example, aircraft range and on-station time, jamming of sonobuoy signals, and vulnerability to other Soviet forces. However, were one to compare submarine- based and air-based ASW on the basis of equally allotted resources, submarine ASW would probably prove second best except in some special cases. The analysis and com­parison need to be made and made in the spirit of best serving the national interest, not the interest of one or another Navy community.

There is a quiet revolution under way in the submarine fleets of the world. The long-range consequences of this render our attack submarines maladapted to their current primary mission. Is then our attack submarine fleet an expensive white elephant? Starting as we must from the threat, are there other missions that can best be filled by attack submarines? Fortuitously, there are. The original submarine mission—i.e., sinking surface ships—is a good one. In addition to quieting their submarines, the Soviets have been building a large fleet of surface war­ships and merchant vessels. Moreover, the new technol­ogy of the cruise missile facilitates long-range land attacks from our attack submarine platforms. If submarines really are better out of the ASW mission, then they should begin to back out of it and concentrate upon those missions best suited to a weapon system that has traded off survivability for stealth. We should make the quiet revolution work for us and consciously structure our submarine force so that it may, unseen, place the Soviet surface vessels and land forces at risk. Using submerged-launched torpedoes and missiles, we can present them with an insoluble tactical, as well as strategic, ASW problem.

’Newspaper articles on the possible role of Argentine submarines in the Falklands Conflict and on the submarine intruder in Swedish waters are cases in point. ²There is another long-range phenomenon that penetrates sea water without signifi­cant attenuation, but it also penetrates the whole earth without significant attenua­tion: the neutrino. To illustrate the difficulty in detecting neutrinos, a detector of the copious amounts of neutrinos produced by the nuclear reactions in the sun is in operation at the bottom of a gold mine in North Dakota. It uses several hundred thousand gallons of a chlorine bearing chemical to detect less than ten interactions over a period of several months. Practical detection of a reactor by emitted neutri­nos is highly unlikely. Moreover, non-nuclear submarines do not emit these parti­cles.

³William D. O’Neil, “Technology and Naval War” (Washington, D.C.: Depart­ment of Defense, 1981), p. 43. This is a compilation of several articles that ap­peared in Military Science and Technology in 1981.

⁴Ibid., p. 4.

⁵For other estimates, see Art Van Saun, “Attack Submarine: The Hidden Per­suader” and Norman Polmar, “Attack Submarines—Pro and Pro,” Proceedings, June 1982, pp. 100-103 and pp. 121-122.

Lieutenant Commander Chatham currently serves as Military Assistant to the Defense Science Board. He received a regular commission through NROTC at the University of Kansas where he graduated with highest distinction in engineering physics. Selected as a Burke Scholar, he spent a three-year submarine tour ending as engineer of the USS Barbel (SS- 580). He then earned a PhD in experimental (laser) physics from the University of New York at Stony Brook. Prior to his current tour with the Defense Science Board, he served as operations officer and navigator of the USS George C. Marshall (SSBN-654). He won first prize in the 1978 Vincent Astor Memorial Leadership Essay Contest, and he has contrib­uted, off and on, to the forum since then. In 1981, Lieutenant Com­mander Chatham was designated Qualified for Command of Submarines.