The Soviet Union is clearly the most active submarine producing nation in the world. It is building new submarines at a rate more than twice that of the United States. Moreover, the popular concept that the Soviet union is “technologically inferior” to the U.S. in submarine design is being challenged by many people, both inside and outside the Department of Defense. They cite improvements in the submerged speed, depth capability, maneuverability, and stealth of the latest Soviet submarines, as well as the innovative designs of the ALFA, OSCAR, UNIFORM, TYPHOON, MIKE and SIERRA Classes, as evidence that Soviet submarine design has come of age from a scientific and technical perspective.
Soviet submarines differ from their U.S. counterparts. One major difference is that the USSR continues to build submarines of double-hull construction, a practice abandoned by the U.S. in the mid-1960s. Critics of Soviet technical prowess and innovation cite this fact as evidence of extreme conservatism by Soviet submarine designers. Ironically, writings appearing in the Soviet technical and military literature explicitly challenge the wisdom of the u.s. practice of building single-hulled submarines.
A discussion of the Soviet rationale for building double-hulled submarines can determine whether the Soviet Union is bound by “design inheritance” as some critics maintain, or whether the USSR has developed a sound philosophy for continuing to use a traditional submarine design.
Combat Survivability: A Soviet Perspective
According to the American Heritage Dictionary, invulnerability has two definitions. The first listed is “immune to attack”; the second is “incapable of being damaged.” The duality may be seen in the usage made of the word by the U.S. and Soviet submarine communities. The u.s. relies upon the first definition to proclaim that its submarines are invulnerable; the Soviet Union applies the more stringent criterion dictated by the second definition.
From a u.s. perspective, an invulnerable submarine is undetectable and therefore “immune to attack” by enemy forces. If safety and reliability are also present, then the submarine is invulnerable to accidental damage caused by man and elements of nature. With these features in hand; i.e., stealth, safety, and reliability, the U.S. may be content to declare its submarines invulnerable.
The Soviets’ view of invulnerability is different. It is dictated by the second definition. For the Soviet, it is inadequate merely to reduce the probability of attack through increased stealth, but the possibility of attack must be recognized and anticipated.
According to several Soviet authors, combat survivability, “the ability to withstand combat and accident damage and restore and maintain combat capability,” is a basic characteristic of a submarine and must be provided for during the period “of a ship’s construction, in the process of day-to-day opertions, during repair, and even when in mothballs.”
Combat survivability, according to the Soviet philosophy, has two major aspects; defense of the submarine against the initial effect of weapons and munitions; and “staunchness” of the submarine to secondary damage caused by fires and flooding. This philosophical difference between the u.s. and Soviet submarine designers explains the rationale behind Soviet Rear Admiral-Engineer V. Droblenkov’s claim that “foreign specialists fail to provide their new ships with adequate survivabilty to withstand the harmful effects of contemporary and especially prospective weapons.” He claims that foreign specialists “think that damage control should be provided only against accidental damage not. associated with weapons effects,” and that “they see no semantic difference in the ~ncept.s of reliability, safety and survivability. ”
Admirals S. Gorshkov and V. Droblenkov, discuss in their writings the “eternal struggle” between trends in the means of desJruction and trends in the protection of warships. They argue for balance. Droblenkov is extremely critical of U.S. submarine design trends, noting that “the balance between the characteristics of survivability and performance, which had been achieved in the process of the century long evolution ‘J.f submarines, have turned out to be disrupted.” He goes on to state that although the more recent U. S. nuclear-powered submarine classes have improved weapons systems, can dive deeper, and have higher submerged speeds, “no qualitiatively new , radical solutions in providing for the survivability of submarines have yet been made.”
According to Droblenkov, the U.S. in 1959 conducted a practical experiment to build a submarine with both surface and underwater survivability. He asserts that the double-hulled TRITON with its eleven compartments, and 36 percent reserve buoyancy represented the last u.s6 attempt to build a highly survivable submarine.
While this interpretation of the rationale for the TRITON’s design may not be correct, this example does highlight the overriding concern afforded submarine survivability by Soviet naval officers writing in the military and technical literature.
Soviet Rationale for Double-Hulled Submarines
Several reasons have been given for abandoning double-hulled submarine construction in the U.S. The major argument is that for a given military capabiltiy, a double-hull design would result in a larger hull. This, in turn, would increase the drag of the platform, and thus require a larger power plant to maintain the same military capability. This argument is valid given the premise that combat survivability has only minimal military utility.
According to the Soviet literature, the benefits accompanying the use of a double hulls fall into the following categories: increased survivability, increased useful volume, reduced costs, and signature reduction. Increased survivability occurs for many different reasons. First, the external hull will cause many weapons to be detonated away from the pressure hull, thereby reducing the impact of explosion. To complement this effect, it will also be possible to install special armor between the two hulls, which along with the equipment and various associated supply lines will further absorb the shock of an explosion.
Increased survivability is also more available in a double-hulled submarine in that the added possibility for ballast tanks allows a damaged submarine to not only remain neutrally buoyant but also to maintain trim. A trouble-hull design permits the use of external stiffeners for framing, rather than internal stiffeners used in a single-hull submarine. This leads to a space savings within the pressure hull and relaxes the requirement to smooth these frames, since they are external to the pressure hull. Air bottles, auxiliary propulsors, heat exchangers, and additional tankage can be stowed between the hulls, thereby freeing additional internal volume for other uses.
The Soviets also discuss placing highly flammable materials between the hulls to avoid the secondary effect of explosions. They claim that weapons can alao be placed external to the inner pressure hull. For example, torpedoes and mines can be launched silently by dropping them out of bomb-bay type hatches in a manner similar to that of bomber aircraft.
Double-hulled submarines also provide several opportunities to reduce costs. In the first place, the exterior hull, which is not a pressure hull, may be constructed of much thinner plates. Since shaping of the exterior hull is hydrodynamically important, the necessary shape can be more inexpensively formed in the thinner outer hull material of a double-hulled submarine. The inner hull or pressure hull can then be formed in the structurally desirable shape of a cylinder, which is also easier to achieve and better adapted to pressure deformation due to increased depth.
A further cost benefit occurs in that, if there is sufficient standoff distance between the two hulls, many future advances in technology may be simply retrofitted. Since many types of equipment may be located outside the pressure hull, the opportunities for retrofitting may occur several times during the useful life of the submarine.
Advanced technologies include various boundary layer control (BLC) schemes such as polymer ejection, suction, controlled heating of surface and gasification. The increased volume existant in a double-hull design affords the opportunity for the Soviets to incorporate and refine BLC systems on existing hulls. These BLC techniques have the potential of radically enhancing the military capability of the submarine at relatively low cost.
Signatures can be reduced through the installation of degaussing coils between the hulls, baffling against radiated noise, the use of internal coatings on the exterior hulls, and by the use of BLC. These methods are most easily employed on a submarine of double-hull construction.
The Cost of Increased Survivability
The argument most. frequently used to challenge the value of a double-hulled submarine is that a larger submarine must be built for a given military capability.
This need not necessarily be true. In a simplified case in which a submarine is approximated by a right circular cylinder, the volume (V) or displacement is given by Π r2 L. The wetted surface in terms of the volume of a submarine can be expressed as:
From the equation it is seen that a single-hulled submarine with a displacement of 3000 t~ns will have a wetted surface area of 1711 meters if the length-to-beam ratio is 11. This ratio is generally representative of U.S. submarines.
From the same equation, a double-hulled submarine having exactly the same wetted surface area will have a 28 percent increase in submerged displacement over th~ single-hulled submarine discussed above if the /D ratio is reduced to 7. Thus, in this case drag of a double-hulled submarine can be similar to that. of a single-hulled version; and, in addition, have a standoff distance of about 0.4 meters to enhance survivability.
Furthermore, the external non-pressure hull can be designed to optimize the hydrodynamic shape of the vehicle. It is more difficult to do this for a single-hulled submarine. since the thick pressure hull sections themselves would have to be shaped. A double-hull thus eases fabrication of the pressure hull, which can be simply a right-circular cylinder.
Furthermore, it can be shown that the cost in terms of speed, for example, for the ALFA to have a double vice single hull is modest.
The benefits afforded by a double hull accrue to the ALFA at a cost of approximately two knots. That is, a single-hulled ALFA could theoretically achieve speeds in excess of 44 knots given a single-hull design. In that at 42+ knots the ALFA is the fastest submarine in the world, there appears to be some wisdom on the part of Soviet submarine designers to trading off speed to enhance the combat survivability of this high value platform.
The longstanding and widespread Western perception that Soviet submarines are noisy and readily detectable may be due to the Soviet Navy emphasizing primarily combat survivability in their submarine designs. This insurance policy seems to have serendipitously provided Soviet submarines with a lengthy list of enhanced performance capabilities not enjoyed by their less survivable single-hulled counterparts.