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XA.mphibious forces have been a major factor in the worldwide influence exercised by the United States during the 20th century. The presence of a highly capable Soviet submarine force gives cause to question the survivability of an amphibious task group in a general, nonnuclear war. Fast-moving nuclear-powered submarines carrying terminal, perhaps wire-guided, homing torpedoes and antiship cruise missiles with an over-the-horizon and underwater launch capability, make U.S. surface combatants more vulnerable to the submarine threat than they have ever been.
Estimates vary as to the size and capability of the operational Soviet cruise missile and fleet submarine force. However, the size of the force is generally acknowledged to be considerable, and it is highly probable that it would be deployed both to protect strategic objective areas and to interdict enemy surface combatants in transit to such areas. These submarines are capable of launching accurate torpedo attacks, launching missiles from within 30 miles of a surface target while submerged, or launching missiles from more than 200 miles away while surfaced.
In planning task group defenses against the submarine, the torpedo and cruise missile need to be viewed as a highly complementary twofold threat, subsurface and air. Tactical task element dispersion and/or concentration to counter one threat can be inimical to defense against the other. However, the ways that the use of these weapons can be limited by constraints on the submarine are just as important as their performance characteristics.
Consider the problem of getting an amphibious task group to an objective area in the face of a Soviet submarine threat. Table 1 is a breakdown of pertinent warfare capabilities (excluding embarked V/STOI. [vertical or short takeoff] aircraft) that could be brought to bear by a representative amphibious task group composed of an amphibious assault ship (LFH), an amphibious transport dock (LPD), a dock landing ship (LSD), an amphibious cargo ship (LKA), and two tank landing ships (LSTs).
Given the threat, immediately apparent is the total lack of antisubmarine warfare (ASW) capability, the limited antiship missile defense (ASMD) capability, the marginal and almost completely overt surveillance capability, and the unsatisfactory electronic warfare (EW) capability. The ultimate conclusion
Table 1 Task Group Warfare Capability
| LPH | LPD | LSD | LKA | LST |
Surface | Four 3-inch/50 | Eight 3-inch/50 | Eight 3-inch/50 | Eight 3-inch/50 | Four 3-inch/50 |
Warfare | rapid-fire guns | rapid-fire guns | rapid-fire guns | rapid-fire guns | rapid-fire guns |
Antiship | Two basic point- | — | — | — | — |
Missile | defense missile | — | — | — | — . |
Defense | system launchers | — | — | — | — |
Electronic | Electronic | Electronic | — | --- . | — |
Warfare | support measures | support measures | — | — | — |
Radar | Surface search Air search | Surface search Air search | Surface search Air search | Surface search | Surface search |
Speed | 23 knots | 21 knots | 20 knots | 20 knots | 20 knots |
(Note: Taken from Jane's Fighting Ships: 1977-78, pages 612-616. Use of this information from an unofficial source should not be construed as an endorsement of its accuracy.)
must be that once the unescorted amphibious task group is detected, it cannot defend itself against a Soviet submarine threat.
Obviously the answer is to provide the supplementary ASW protection required. However, the accurate attack ranges afforded the Soviet submarine force are so great as to require an excessive number of escorts for the protection of a minimum number of task groups, convoys, and main body units. By the time task groups and convoys were formed and escorts parceled out, an amphibious task group commander may have to get a landing force through the open ocean to an objective area without direct antisubmarine support.
This is not to say that indirect support from broad-ocean ASW forces—fixed surveillance systems, long-range ASW aircraft, and hunter-killer groups—will not be available. As in previous wars, the United States will depend on sea-lanes for transporting critical war materials—the supplies and equipment which will be used in combat. To protect long sea-lanes from submarine interdiction over a prolonged period, it will more than likely be necessary to employ a portion of available assets in some type of broad-ocean ASW force, as opposed to escorting each task group, convoy, and main body unit. Such forces would provide a measure of indirect ASW support to the unescorted amphibious task group.
Avoidance, cover, deception, and stealth rather than engagement are essential to the survival of the unescorted task group. Given sufficient latitude, task group planning can be directed toward reducing the probability of detection by enemy forces during transit. Areas known to be covered by Soviet air and satellite surveillance can be avoided to the maximum extent practicable. Meteorological forecasts can be used to take advantage of adverse weather conditions, both to reduce the probability of detection by direct surveillance and to reduce the effectiveness of satellite surveillance.
Intelligence gathered from U.S. surveillance systems (SOSUS, high-frequency direction finding, ASVf patrol aircraft, etc.) can be used to avoid areas of probable submarine location. Oceanographic environmental data can be used to estimate water propagation conditions and probably enemy passive sonar detection ranges. All this information can be made available by radio broadcast to the amphibious task group commander operating under strict emission control.
By considering the threat relative to the submarine’s needs and constraints in effectively delivering a weapon, vulnerabilities in her tactics can be identified and exploited in planning defensive measures. Prior to delivering an attack the submarine must first search for, detect, classify, and approach the target.
During the search phase, information sources available to the submarine’s sensors are passive intercept of radar, communications, and acoustic emissions; visual sighting; active radar or sonar search or both; and passive sonar intercept of propulsion noise- Detection ranges afforded the submarine’s visual, radar, and active sonar search are beyond the control of the task group commander and are generally too short to provide an effective broad area search for targets in transit. In addition, these search modes could compromise the covert nature of the subma-
Once the submarine detects the task group, she is Oore than likely to commence an approach, attempting to classify and resolve the individual targets, mission and speed control also affect classification.
rine s operations and enhance the probability of deletion by broad -ocean, indirect-support ASW forces.
Two important long-range sources of information available to the searching submarine are high- frequency communications and search radars. Passive lfitercept ranges on these extend well beyond the horizon and provide good bearing information, although range may be difficult to estimate. With ASW escorts present, the active SQS-26 sonar provides c°mparable passive detection ranges to the enemy submarine with no classification problem.
Use of radio, radar, and active sonar is fully controllable by the amphibious task group commander. Strict control of all these emitters would completely eliminate the submarine’s passive detection opportunity- If, for some reason, strict silence is not accept- ahle, some form of random emission schedule can be employed, thereby reducing the effectiveness of random-interval submarine passive search. Even if the submarine elects to search continuously for electromagnetic signals, only intermittent information whl be available, thereby reducing detection opportunity, complicating the classification and fire con- tr°I problem, and requiring sustained operations at a tUpth not conducive to effective passive sonar search. Additionally, this will require exposure above the Surface of some part of the submarine’s structure, thus enhancing the probability of detection by 'ndirect-support ASW forces.
The remaining long-range information source available to the submarine is propulsion noise. A ship’s radiated acoustic noise provides a continuous ■^formation source that can be used for direction 'tiding with good accuracy. Detection ranges are 'fihly dependent on a ship’s speed, and one travelog faster than 20 knots can be detected acoustically at very long ranges. Movement at 10-15 knots produces little noise, is comparable to that of many Otrchant ships, and is non-identifying. Emission c°ntrol policies have no bearing on the effectiveness the enemy’s passive sonar. Thus, the task group Can be detected at greater ranges the faster it is go- ,n8- To the extent that detection ranges are determined by speed, they are controllable by the task jT°up commander. To limit task group detection to °nzon ranges against a submarine, all electronic and acoustic emissions should cease, and all ships should e kept below cavitation speed. As these controls are Olaxed, the detection ranges afforded a submarine 'ncrease.
If emission control has been effective, then no emitters exclusively identifiable to U.S. surface combatants have been detected, and the submarine, if outside periscope range, must depend completely on acoustics for classification. The disadvantage of depending on acoustics is the possibility of deception and masking. Any controls that deny or disguise characteristic combatant acoustic signatures will confuse the picture to the submarine, thus denying positive long-range target identification.
The significance of denying positive long-range identification to the submarine can best be understood if one considers that there are more than 50,000 vessels plying the oceans of the world. Only a very small percentage of them could justify expenditure of a high-cost, long-range antiship cruise missile which is available only in limited quantities. Furthermore, the political considerations involved— the alienation of neutrals—will probably discourage indiscriminate missile firing. Thus, the submarine is faced with essentially two alternatives: closing the contact for positive identification or classifying it as nontarget and resuming surveillance. Depending on such factors as range, relative speed, and mission constraints, the former might not be an available option.
This suggests that the best chance for survival lies in steaming the unescorted amphibious task group quietly and covertly, at moderate speeds, in widely spaced random formations which change course randomly to complicate the submarine’s classification and tracking problem. Advantage could be taken of the cover against surveillance provided by rough weather and the acoustical interference and confusion generated by ocean traffic. Without the obvious label of combatant, the task group becomes perceivable as no more than a few ships moving.
While these tactics may be successful against a single or multiple submarine threat, introduction of air/submarine targeting, or the possibility of vectored attack by outside means, greatly reduces the submarine’s detection and classification problem. Undoubtedly, some ASW capability is required to ensure a reasonable probability that the task group will arrive in the amphibious objective area. But how much is enough? Unfortunately there is no clear-cut answer to this question. It does, however, raise two interesting tactical considerations. Does the sailing of the task group in tight formation serve to maximize ASW protection? And, is task group protection best effected in an active, overt mode of operation? The answers to these questions will affect the number and type of ASW assets required.
Bearing in mind both the submarine’s inherent
In a wartime situation, U.S. amphibious warfare ships might take aboard antisubmarine helicopters as the USS Guam (LPH-9) did with this SH-3A Sea King during interim sea control ship trials in 1972.
constraints and the capabilities of her weapons, arguments against tight formations are many. Bunching of main body ships provides ready, long-range identification of targets and a favorable opportunity for coordinated attack. If escorts use passive acoustic measures, the noise of many ships traveling close together interferes with, and may preclude, passive detection of the submarine. If active acoustic measures are used, the combination of massed shipping plus active sonar provides submarines the opportunity for long-range identification and increases the likelihood of mutual interference.
In favor of tight formations in a conventional war is the possibility that incoming missiles may cluster on a single target, preventing destruction of many. Tight formations can also provide an added degree of close-in defense against missiles. However, the high speed of the missile and short warning time available would seem to preclude anything more than last- ditch self-defense. Shooting down an inbound missile headed for a main body ship several miles away requires a level of anti-missile capability not generally found on board the average ASW escort. Hence, with the longer submarine attack ranges available, close groupings of ships and concentrations of escorts will more than likely not produce the lethal prosecution of close-in submarine contacts for which tight ASW formations are designed.
With overt modes of operation there is the likelihood of tight, identifiable formations, thus evoking many of the arguments already noted. Active sonar tends to identify valuable targets at great ranges, thus enhancing the submarine’s advantage. For the closer in torpedo attack, the advantage is not so great. However, the submarine attacker has been alerted to the precise location of the defender, and is thereby encouraged to use water conditions and aspects most likely to minimize active acoustic detection. Both attack and evasion tactics will be carefully based on sound velocity profiles, gaps in the coverage, mutual interference, and the susceptibility of active sonar to false contacts from wakes, sea life, and countermeasures. In short, the attacking submarine is forced into modes of operation where she becomes less susceptible to either active or passive detection, with no appreciable reduction in attacking capability.
What seems to evolve is that traditional noisy employment of ASW escorts in the open ocean allows
submarine missile launching from ranges beyond the sea control capability of the escort. And, since close' in escort defense of main body ships against incoming missiles seems impractical, the missile threat alone tends to drive amphibious task group movement toward dispersed, quiet, deceptive, covert, and passive tactics. But, and this can’t be emphasized enough, passive tactics as a counter to the submarine weapon system are meaningless if the task group is s° overt because of numbers, formation, and propulsion noise that it generates an unprotectably large attack area in the ocean. Hence, decreasing the area of required sea control, increasing the area of ASW coverage, and maintaining anonymity are the keys to secure task group transiting.
How, then, can this be accomplished for the amphibious task group under consideration? Intelh' gence from U.S. surveillance systems can be used to avoid known areas of probable submarine location' Avoidance rather than prosecution of anything other than immediate high-threat contacts is preferred in order to maintain anonymity.
Where available, long-range patrol aircraft can he employed to extend the task group’s ASW and surveillance capabilities. As with other ASW assets, assignment of the patrol aircraft is complicated by the omnidirectional nature of the open-ocean submarine threat. When a threat axis or threat sector exists* first consideration should be given to coverage ^ that direction. Given a direct support role, the patrol aircraft is capable of providing acoustic detection barriers far ahead of the task group, alerting and possibly diverting movement from a submarine threar area. Furthermore, patrol aircraft can prosecute contacts without compromising the position of the task group.
Sea-based, fixed-wing ASW aircraft could be employed in essentially the same mission at shorter ranges from the task group. However, it is not likely that ships capable of supporting fixed-wing ASW aircraft operations would be dedicated to a small amphibious task group. They would probably achieve * greater payoff if employed in some form of reactive
broad-ocean ASW mission, or in a transit lane convoy protection role, from which a measure of indirect Support would be provided all transiting task groups.
Only recently has it appeared necessary to employ the ASW capabilities of the attack submarine in direct Support of other naval forces. This development sttMs directly from the advent of the cruise missile threat. Assignment of the submarine in a direct- support ASW role is complicated by command-and- c°ntrol problems, main body noise, and the possibil- 'ty °f mistaken identity and/or mutual interference from surface ships and aircraft also assigned to the task group. Nevertheless, the attack submarine is the host ASW weapon in our inventory and can be as- S|gned a sector close to the main body for conducting sprint-and-drift tactics or to an area ahead or behind the formation. With two escorting submarines, one tould be assigned an area ahead and the other behind, or both could be used to increase the coverage °f the area ahead of the formation. In any event, the taPabilities of the submarine fit nicely into providing aclditional ASW defense in depth and filling the gap between longer range land- and sea-based air cover- a§c\ and shorter range coverage by ASW helicopters a°d surface escorts.
Frigates equipped with SQS-26 hull-mounted sonars, variable-depth sonars, towed acoustic linear arrays, ASW Navy tactical data systems, and LAMPS fbght airborne multipurpose system) helicopters represent the most capable ASW surface ships available. G'ven the size of the amphibious task group to be Protected, four such frigates, two with towed arrays, "'°uld seem to be an acceptable minimum for a Moderate-speed transit. Disposition alternatives, not only for surface escorts, but for all ASW ships and aircraft assigned, will be determined principally by th(-' capabilities and limitations of their acoustic s°nsors—by the fig ure of merit and effective sonar range for each system configuration. The area of ASW c°verage available is an indicator of the area within "bich the task group commander can exercise sea c°ntrol against the attacking submarine and will thus a*So influence main body separation and disposition.
based on the threat evaluation, main body disposi- tlQn, and ASW coverage available, surface escorts |°uld be assigned to a moving barrier, wolf trap,
r8e area sectors, or close-in screens. Tradeoffs be- tVVeen assignments may be available. A frigate wdth a t()Wed array may provide a sufficient figure of merit cn cover a “delousing” sector astern of the formation,
Us freeing a direct-support attack submarine for as- Sl8nrnent out ahead of the task group.
LAMPS helicopters can be employed in a variety of Missions including ASW, antishipping surveillance tactics, and, when necessary,'communications relay. LAMPS provides the frigates with a standoff ASW kill capability. The requirement to maintain a quick helicopter reaction capability for extended transit periods would seem to indicate limiting LAMPS flying time to actual threat response. These helicopters can be maintained on deck in varying degrees of readiness from launch within five minutes to launch within 30 minutes. Once launched, LAMPS can be used effectively for localization, classification, evaluation, and attack. Another option available to the task group commander is the employment of SH-3 ASW helicopters from the LPH, or for that matter from any of the amphibious ships. This would involve a tradeoff in amphibious lift capability. The SH-3, while not so technologically sophisticated as LAMPS, has the added benefit of longer mission times and a dipping sonar capability. It is also a candidate for a sector screening assignment.
Regardless of the number and type of ASW assets available, the task group commander is principally interested in reducing to a minimum the amount of ocean he must control, increasing'to a maximum the area of ASW coverage, and remaining undetected. Given the nature of the ocean’s acoustic environment, as well as the nature of the submarine- launched cruise missile threat, active, overt, and noisy ASW measures seem less promising than passive- acoustic and electronic tactics. By using passive tactics, the task group commander forces the submarine to take overt action in order to deliver an attack successfully, and this creates a tactical advantage not only for direct-support ASW units, but also for broad-ocean indirect support forces. Irrespective of the tactics chosen, effective ASW coverage can be achieved only by positioning forces commensurate with their capabilities and limitations, by taking advantage of the synergistic effects of complementary ASW systems, and by designing an ASW defense in depth that produces the highest detection probability for the situation at hand.
Lieutenant Commander Mellin was commissioned in the Navy in 1964 after graduating from Colorado College at Colorado Springs. He then served shipboard tours in the USS Taylor (DD-468) and USS Ault (DD- 698) and commanded the USS Whippoorwill (MSC-207). Following tours as an advisor in South Vietnam, in the Office of the Chief of Naval Operations, and in the Bureau of Naval Personnel, he attended the Naval War College, graduating with distinction from the college of command and staff in 1976. He is now executive officer of the USS La Moure County (LST-1 194). His article “The Amphibious Force: A Ready Political Instrument” was published in the August 1977 Proceedings.