SSNs: Mounting An Offensive Defense

The U. S. Navy is composed of two operating forces. The submarines comprise the nation’s anti-super­power force, dedicated in strategy, tactics, and imposition to deterrence and, if deterrence fails, to the ^c°mplete destruction of the enemy’s sea power. The force deludes fleet ballistic missile submarines (SSBNs), whose single purpose is to deter superpower aggression, and fast attack submarines (SSNs), which can neutralize any sea-based threat below the level of an all-out nuclear exchange. All other elements of U. S. naval forces—from aircraft carrier battle groups (CVBGs) to battleships and Marine Corps infantry units—exist to influence world events in a fashion favorable to U. S. political and eco­nomic goals. They would have little impact in a super­power war at sea.

U. S. Ballistic Missile Submarines

SSBNs constitute the premier element of the U. S. de­terrence triad. The Trident-missile submarines are mobile, covert, responsive, and, with the advent of the D-5 mis­sile, capable of both counterforce and countervalue target­ing. They are the nation’s most important anti-superpower forces. With a programmed level of 21 units, each capable of delivering more than 150 warheads, the U. S. SSBN force has the capacity to become a stand-alone deterrent. In fact, the D-5 missile may obviate the need for land- and air-launched nuclear weapons, but interservice and con­gressional politics will ensure that the air and land legs of the nuclear triad survive. Nonetheless, cutbacks in U. S. defense spending are inevitable, and cutbacks in the strate­gic forces must come in the most vulnerable and least cost-effective forces, the air and land-based assets. As a result of these cutbacks the strategic value of the SSBN force will naturally increase. Indeed, it may be time for the United States to consider increasing its numbers of SSBNs.

Soviet Changes in ASW

The Soviets have long held that their navy exists in large part to support their SSBN forces. The antisubma­rine warfare (ASW) tactics they employ to protect the SSBNs are for the most part reactive or defensive. They sanitize areas where U. S. SSNs may operate and then conceal their strategic assets in these ASW free zones. In addition, they frequently employ a “shotgun” SSN to protect an SSBN directly. This practice, given its relative success, will probably continue.

If we assume that the Soviets recognize that U. S. fiscal constraints will probably cause the United States to raise the relative worth of its efficient strategic assets (SSBNs) while decreasing the worth (probably through reducing the numbers) of the less efficient (air- and land-based) strate­gic assets, then we might further assume that the Soviets’ interest in open-ocean ASW would increase. Because open-ocean search and detection require large numbers of ASW platforms, it is reasonable to assume further that the Soviets might deploy a lot of relatively inexpensive ASW platforms to threaten the sea-based leg of the U. S. nuclear triad. However, a cursory look at developing Soviet pro­grams and force structure does not yet bear this out.

The area with the greatest potential for rapid and possi­bly revolutionary ASW advances is that of space-based stations capable of full-spectrum electromagnetic scanning and active synthetic aperture radar processing. In this, the Soviets enjoy a significant practical lead over the United States. They have a demonstrated capacity in the field of

The Soviet attack submarines have a long tradition of pro-SSBN operations; it may be that U. S. SSNs, like the Omaha (SSN-692), also will be so deployed.

orbital heavy lift. They have for some time maintained a manned orbiter. They have the technologies required to support passive and active exploitation of relevant por­tions of the electromagnetic spectrum. We should not ig­nore this developing capability in any assessment of the Soviets’ ASW potential.

U. S. Attack Submarines

What, then, is to become of the U. S. SSN? Histori­cally, the Navy has used its nuclear attack submarines primarily in a forward ASW role, to deny Soviet subma­rines and battle groups free access to vital U. S. sea lines of communication (SLOCs). This specific mission, as well as the Soviet threat, guided the U. S. Navy in deter­mining how many SSNs were needed.

At one point, wanting a rationale for increasing force levels, the Navy hypothesized a new role for the SSN, that of direct support for the CVBG. This new mission allowed force planners to argue successfully for the production of the Los Angeles (SSN-688)-class submarines, whose suc­cess is evidenced by their numbers.

The current role of the SSN is ambiguous, at best. Re­cent Soviet advances in submarine quieting and acoustic processing have led to serious questioning of the SSN’s effectiveness in any antisubmarine role. While the SSN is clearly effective against surface ASW elements and ship­ping, its ability to successfully detect third-generation Soviet SSNs generally is not known. The utility of the SSN in direct support of the CVBG is questionable. The results of recent fleet exercises surely demonstrate that ASW defense of the CVBG is very difficult. While it ap­parently can defend itself against most air and surface threats, the CVBG is vulnerable to submarines, and post- , ing SSNs as watchdogs does not seem to make it any safer.

Soviets’ attempts to detect and localize U. S. missile sub­marines without external cueing have required more ASW assets than they could muster. Even the most recent tech­nological advances have done little to jeopardize the secu- ^nty of these strategic assets. However, the Soviets have an ^edge over the West in many of the fundamental mathemat- ^lcal and scientific fields, and this gives them extraordinary Potential in areas vital to antisubmarine warfare. The United States needs to anticipate these gains and begin the search for ways of ensuring the Trident submarines’ con­tinued security. One long-neglected possibility is to con- S'der how best to use attack submarines to protect the SSBNs.

One maxim of naval tactics should be borne in mind when formulating weapons employment policy: Attack effectively first. Or as the submariners have it: He who ^lres the first shot will write the patrol report. The Soviets nave violated this offensive principle for years by pairing •heir deployed SSBNs with a duty shotgun SSN, whose ^Very nature is defensive.

Forward ASW operations have long been the hallmark °f the U. S. SSN mission to clear the SLOCs of sea-based Weapon platforms. The attack submarines deploy far for­ward to interdict the Soviets. This forward, offensive ASW posture can also be the key to using SSNs to protect ne missile submarines. The toughest challenge for the . Ns lies in detecting the enemy submarines. At convert- ^lng detection to localization to kill, the U. S. SSN force is ^exPert, but detection is more difficult.

Detecting enemy submarines in the open ocean is per­haps the most vexing problem facing the SSN force today, ubrnarine quieting, rising ambient noise levels, and the °viets’ increased sensitivity to the need to muffle the noise of routine housekeeping practices is forcing the . ■ S. Navy to reexamine its open-ocean search and detec- j'°n practices. Of course, the Soviets face the same prob- ^ern> perhaps in spades, in their efforts to detect patrolling ^“Ns. But as difficult as this situation is, sheer numbers §° a long way toward solving it—numbers and the for­ward deployment policy. By deploying its SSNs well for­ward the Navy can exploit the geographically constrained ransit routes to develop initial detections, localizing and Hling Soviet ASW units before they can join the search ^tor U. S. SSBNs.

Soviet exploitation of space for ASW would not under­^Cut the Navy’s reasons for adopting the forward employ­. ,^ent policy. In even the worst-case possibility—if locat­ing data were continuously available to the Soviets— • S. submarines in a defensive role would be just as ^VuJnerable as those operating offensively. So the Navy ^rrilSht then just as well stay with the more effective for­ward or offensive option.

Forward Employment Policy

The number of SSNs required to protect U. S. SSBNs is °hviously a function of the number of deployed SSBNs ‘^lnd the number of anti-SSBN ASW forces. It also depends whether the SSNs are used defensively or offensively. ^oth options will result in a concentration or funnelling of

anti-SSBN ASW units. In the shotgun role the funnelling would come from units concentrating at the SSBN during the final or attack phase of the operation. In the forward- deployed role this same funnelling occurs because of geo­graphic constraints on egress or transit routes. It seems clear that the latter is a better way to combat anti-SSBN ASW elements. But how does it fare against the ultimate measure of effectiveness—gains in SSBN security per SSN assigned?

A simple employment policy model provides the an­swer. Assume that there is one anti-SSBN ASW unit, one pro-SSBN SSN, and one SSBN. In this extremely simple model a reasonable measure of effectiveness might be the probability that the SSBN will survive an encounter (or one minus the probability that the SSBN would be killed). Mathematically, we write:

1.     Measure of Effectiveness (MOE) = 1 - P_Ssbn kin

Making a number of liberal assumptions, we determine the probability of an SSBN kill by solving for the product of four independent events. Specifically, the SSBN is killed by the anti-SSBN ASW unit if the anti-SSBN ASW unit (a) is not killed during egress or transit to open ocean (1 ^- Pkiii xsit) and (b) detects the patrolling SSBN (Pdetect) and (c) converts the detection into a localization (Pi_OCai) and (d) successfully engages the SSBN or, for simplicity, is not himself killed at the engagement site (1 — P_kin _atck). We rewrite the equation as:

2.      MOE = 1 — (1 — P_kiu xsit)*(Pdetect)*(P|ocal)

*0 Pkill atck)

We are now left with maximizing the MOE with respect to the SSN employment option chosen.

Clearly, if the SSN is forward deployed then the prob­ability of anti-SSBN ASW unit kill during egress or transit is at a maximum. Also, because of the SSBN’s self­defense capability, the probability of anti-SSBN ASW unit kill during attack is greater than zero. On the other hand (and this is the crucial argument), if the SSN is de­ployed in a sljotgun role then the probability of anti-SSBN ASW unit kill during egress or transit is by definition zero. In addition, the combined kill probability of the shotgun SSN and the self-defense capable SSBN is less than their simple sum.

This simple model verifies what we intuitively surmise. The forward-deployed SSN is more effective in the pro- SSBN role than the shotgun SSN. Thus, the SSNs must continue to “attack effectively first” to play their part in protecting the SSBN force—a force destined to become increasingly vital to U. S. deterrent strategy as the nation lessens its reliance on air and land-based nuclear weapons. While the Navy has yet to conduct sizing analysis for this role, SSN employment policy should begin to shift toward a forward-deployed, pro-SSBN role.

Commander Peppe serves on board the USS La Jolla (SSN-701) as engi­neer officer. His previous tours include duty on board the USS Andrew Jackson (SSBN-619) and the USS Groton (SSN-694). He is a past con­tributor to Proceedings.