THE SEMI -SUBMARINE

In a provocatively titled article in the September 1983 issue of the Naval Institute Proceedings, “Sink The Navy I”, Capt. Charles C. Pease carries to an extreme the thesis that the threat posed to surface vessels today and tomorrow, by precision guided missiles and particularly nuclear weapons, dictates a re-examination of the functions of existing types of “maritime platforms”. Where possible, he feels, there should be an evolutionary development in which functions traditionally assigned to surface vessels would be assigned to submarines and “semi-submarines”–specifically designed to carry out such functions effectively and with significantly less vulnerability.

The basic premises that underlie the arguments Capt. Pease advances, and they are wide-ranging, are these:

• for a variety of reasons, including cost and the increasing need for complex and, frequently, large sensors and weapon systems on ships, new constuction surface combatants have not been hardened since the end of World War II;
• during the same period, lethally accurate precision guided weapons have been developed and put into use, by a number of world powers;
• the u.s. has not been able to devise and install a “leak proof” active defense system against such weapons, for her surface forces (Aegis will help significantly, but may not be sufficient);
• U.S. battle formations are vulnerable to nuclear barrage attack. from cruise or ballistic missiles, or a combination thereof. This type of attack. might well be used in a war in which the u.s. seeks to protect sea lanes, or project forces across the sea (e.g., a NATO scenario);
• submarines, and to an extent, semi-submarines are far less vulnerable than surface ships, both in respect to detection in the radar, visible and infrared spectra, and in their probability of sustaining damage.

After examining possible scenarios for battle, primarily as they relate to a carrier battle group, Capt. Pease concludes that there is sufficient cause to re-examine the functions of surface ships in such a manner as to identify systeiiS that could be submerged. Where certain functions are not easily submerged they might be transferred to airborne or spaceborne platforms. But those functions which are not readily re-allocated, Pease suggests, might be packaged in numerous small special-purpose surface vessels whose design would be hardened in such a way as to incorporate extra protection against blast, radiation and electromagnetic effects of near-miss nuclear detonations. He suggests that even these functions might better be packaged in a semisubmersible hull.

“semisubmersible” is a term that has been used to denote several widely different vessels. One, which is non-naval, is a type of drill platform used in offshore oil exploration and production. Another is the “SWATH” (Small Waterline Area Twin-Hull) ship, which provides a remarkably stable platform, and can be designed to operate at relatively high speeds, but in aost versions does not actually submerge. In hie article, Capt. Pease, however, used the term “Se~submersible” to describe a vessel with low freeboard which normally operates on the surface, but can submerge to shallow depths for concealment or protection. He further envisages its super structure to be possible in a truncated pyramid for., with sloping armored sides, which can deflect projectiles, missiles, and fragments–a hull-form remarkably similar to that of the Confederate ship VIRGINIA, the ex-MERRIMAC.

Essentially, this modern seaisubmersible would be an AAW support vessel, fitted with radars, SAM aissiles, and, presumably ASW weapons as well, although these last are not aentioned in the article.

But first in the evolutionary process of “sinking the Navy” Pease feels that certain new submarine types can readily be produced: a fleet auxiliary tanker to be used primarily for replenishing carriers with jet fuel; a subaarine aauaunition and dry stores ship; and eventually a submarine aircraft carrier using V/STOL aircraft. Most of these vessels have been propsed at one time or another in the past. In aome cases they have had the benefit of considerable design study. But none has been built.

Whether a semisubmersible AAW vessel modelled on CSS VIRGINIA, as illustrated in the Proceedings article, is in fact feasible, and what its speed, range, seakeeping ability and other characteristics might be, are difficult to judge  without  study-or at least without more design information than has been provided. Capt. Pease however asserts flatly that there is no technical reason why such vessels could not be produced  within the next few years.

Navy planners, designers, and tacticians might well consider the desirability of other semisubmersible ship types, with different missions as well. Some, with characteristics, and missions quite different from those envisaged by Capt. Pease have been suggested in the past and studied to the point of conceptual design. Such designs were considered producable.

One such design was conceived as a unit capable of very high transit speeds. It combined a submerged body of revolution, similar to the modern SSN hull, with a small “bridge” structure above the waterline supported by a strut structure connected to the underwater hull. The strut structure kept the hull at a depth of over three times hull diameter to eliminate the drag from surface wave action. This arrangement also made possible use of an air supply system for normal operation. The vessel could thus be powered by an air-breathing propulsion system–either gas turbines, diesel, steam turbines, or some combination form of propulsion. The bridge structure would provide facilities for navigation, communications and sensing systems. Crew quarters, weapons, stores, fuel, and auxiliary machinery would be below in the main hull. (See illustration). Of primary attraction would be its capability to button up and submerge on battery power for short periods of time–to get away from surface missile attack or the effects of nuclear air blasts.

One tentative design for an experimental test craft of this type had the following principal characteristics:

*In a near-surface mode.

This selli-submarine, or semi-submersible, was basically a near-surface craft. Its design was based on the same principle as that of the “SWATH” ship, although it did not have twin hulls, Its principal advantage, high transit speed, as compared with the speed of other ships of similar length, resulted from this design, which takes advantage of minimizing wave resistance.

The dimensions, capabilities and characteristics of an operating combatant unit of this type would be somewhat different from those listed for the test model, and would be dependent on the mission, or missions chosen for it. the originators of this particular seadsubmarine concept, first advanced in 1960, thought of it primarily as an ASW vessel designed to operate in forward areas. They believed it might also be useful for certain types of mine-sweeping, although its suitability for this task was not explored in depth. The advantages claimed for this semi-submarine were its high transit speed, its enhanced ability to avoid rough weather conditions, its ability to remain on station for comparatively long periods of time, and its decreased vulnerability, as compared to surface ASW vessels.

Nearly ten years later, a somewhat similar design, also a semisub~~arine, was studied in greater detail. This vessel was intended as an ASW platfora, but was also usable in anti-shipping llissions. It was conventionally powered (i.e., non-nuclear), of relatively saall size (about 1 , 200 tons) , and armed with torpedoes . Its crew was small–in the range of 28 to 30 men.

Whereas the earlier semi-submarine design relied heavily on the hydrodynamic characteristics of the semi-submersible hull with a surface-piercing strut, and optimized for speed, the later design was optimized for ASW effectiveness on station. It too envisaged the use of gas turbines. They were located in the super-structure for propulsion in the seai-subaerged 110de of operation. However only about 3,000 HP was provided with a resultant transit speed of only 24 knots. On the other hand it was to be fitted with enough silver-zinc batteries to generate 400 HP for a high submerged speed and a submerged endurance of some 250 miles at 4 knots. Furthermore it was designed for moderate submergence depths, not just for shallow subaergence only.

The later design provided tanks to carry fuel sufficient to provide a range of 7,000 miles, and an endurance of 45 days.

Considerable thought was given to making this vessel an effective ASW platform. Her designed depth capability made it possible for her to go below the normally encountered thermal layers. And, the placement of main propulsion and battery charging power high in the sail sharply reduced radiated noise in the surface mode. Provision was made for a conformal sonar array in the bow and for streaming a towed line array. Importantly 1 this vessel could close targets detected by sonar and use attack evasion tactics at a maximum submerged speed of 21 knots for 1 to 2 hours.

For armament 1 the ASW semi-submarine was to carry about a dozen lightweight ASW torpedoes, and a mix of heavyweight torpedoes and anti -shipping missiles. The mix composition was variable, depending on the specific mission assigned.

This semi-submarine was studied in far greater detail than the earlier, fast-transit concept, and seemingly in more detail than the AAW semi-submarine envisaged by Capt. Pease. However, like so many of the ship types suggested in .. Sink the Navyl.. it requires further study before possible adoption. The idea of a semi-submarine AAW unit also deserves attention.

Such studies should carefully examine intended mission, mode of transit (i.e., whether in company with a task force or peroceeding independently), range, armament, armor 1 and other pertinent characteristics. The study should include both types of semi-submersible: those that submerge for mission effectiveness, and those that normally operate surfaced with low freeboard–which submerge only to escape detection or reduce vulnerability. It should include consideration of whether the semi-submersibles should be single-purpose, or multi-purpose. If the former seeu desirable, a “family” of semi-submersibles with different configurations for different missions might be built.

This study might well be part of a larger study which examines all Navy ship types including subaarines, as to their vulnerability and also their effectiveness (if not cost-effectiveness). Vulnerability considerations should include not only vulnerability to precision guided llissiles and nuclear attack, but also vulnerability to torpedo attack and to mines. This large study should consider the interaction of existing and proposed ship types in task forces or battle groups, including the implications of having task forces of mixed composition, surface and semi-submersible. It should include consideration of the advantages, costs and possible drawbacks of using submarines for wholly new roles, in particular those briefly discussed in Capt. Pease’s article. Finally, it should include the use of semi-submarines in ASW roles.

Capt. Pease is right in this premise: we are in an age of transition in Naval warfare and we cannot sit by complacently trusting in the effectiveness of our present fleet units. We do have fine ships, trained men and good weapons. But we have to examine these assets in the light of today’s warfare environment. Recognizing present enemy capbilities, we apparently should be prepared to effect changes.

Victor T. Boatwright