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The Peoples Republic of China (PRC) entered the nuclear-powered submarine field in the 1970s with the introduction of the HAN nuclear-powered attack submarine. In 1981, the PRC introduced the XIA nuclear-powered ballistic missile submarine. The  HAN SSN  design appears  to  be  based  on  the u.s. ALBACORE diesel-electric submarine design, while the XIA SSBN design seems to be based on the Soviet YANKEE, or U.S. GEORGE WASHINGTON SSBN design.

At sea photography indicates that both submarines are of double-hull construction. It is significant that the PRC chose to build double-hull nuclear-powered submarines, rather than follow the West’s lead and build single-hull nuclear-powered submarines. Other PRC submarines, such as the Soviet designed ROMEO diesel-electric submarine and the Soviet designed and built GOLF diesel-electric ballistic missile submarine are also of double-bull construction.

A review of PRC submarine design literature indicates that PRC naval architects embrace the Soviet concepts of submarine combat survivability. This is not surprising since the Soviet Union had an early and apparently profound influence on PRC submarine programs. PRC . submarine design litera-ture strongly suggests that the HAN SSN and XIA SSBN incorporate post-attack combat survivability similar to those built into Soviet submarines.

Below are several quotations (along with the author’s comments) extracted from a PRC book titled “Fundamental Knowledge of Submarines,” which illustrate Chinese submarine combat surviva-bility philosophy.

In a discussion of post-attack combat survivability or what the PRC naval architects call the “Maintenance of Combat and Mobility of Submarine After Being Attacked,” satety Radius is defined as: “··· the shortest distance from the center of an explosion of an anti-submarine weapon to the submarine body and its equipment so that the explosion effects will not harm the main combat capacities defined by tactical technical requirements.” Bote that this definition corres-ponds to the Western definition of “sate standoff range” and the Soviet definition of “safe radius.” PRC naval architects, moreover, state that a weapons survivability design criteria is con-sidered during the very early stages of a submarine design.

Danger Radius or Critical Radius is defined as: “··· the shortest distance from the center of explosion of an anti-submarine weapon at which the damage inflicted upon the submarine body, machinery and crew causes the submarine to lose its combat  capacity,  but  the  submarine  can  still float on the surface.” This definition corresponds to the (currently in vogue) Western definition of “mission kill.” In this case, the submarine cannot remain submerged because personnel are injured, equipment is seriously damaged (shook, fire, flooding), and the pressure hull is damaged (dented, ruptured, or with a hull penetration). According to the Chinese, “the safety radius and danger (or critical) radius are the major specifications concerning the resistance of a submarine to anti-submarine weapons. Improvements of the submarine’s resistance to explosion of anti-submarine weapons means shortening the safety radius and danger radius.” This suggests a requirement to improve post-attack survivability by increasing hull strength and equipment shock hardening, and improving damage control.

Some further guidance is supplied: “Structural strength and rigidity of the submarine body , the danger radius of a nuclear explosion should be used as the basis of calculation, and the structural strength of the submarine body should be near the value required by the para-meters of the danger radius.” This is a very important point. PRC submarine designers believe that a pressure hull should be designed to with-stand both hydrostatic loading and dynamic (i.e., underwater explosion) loading. Apparently, dynamic loading criteria “drives” PRC pressure hull design. Dynamic loading criteria is very probably based on underwater nuclear weapon effect parameters.

Submarine Survivability is defined as the: “··· ability to maintain combat force and cruising performance during both daily (peacetime) duty navigation and combat tasks.” Then the two types of submarine survivability are discussed. Daily (Peacetime) Survivability is “··· the submarine’s ability to carry out normal operations under unfavorable natural conditions, such as sway caused by wind and waves, vibration, corrosion, and operational abrasion or mechanical parts. Daily (Peacetime) survivability is guaranteed by the performance of the various parts or the submarine.” And, Combat Survivability is “··· the sub-marine’s ability to protect itself from serious damage in performing combat duties.”

In a discussion or measures to improve submarine survivability, the following quotes are or interest: “Tactical and technical measures (to improve submarine survivability) include improve-ments in the submarine’s concealability, mobility, seaworthiness, unsinkability, defenses, etc . In addition, the ability or the technical equipment itself to survive is also extremely important and can influence the manifestation or the total submarine performance. Therefore, improvements or the survivability or equipment must be taken into consideration in the design and type-selection phase or the submarine. The basic regulation is that the function or any piece or equipment, under normal conditions, should be able to be taken over by at least two (other) means.” Note that PRC submarine designers and naval personnel believe that “survivability” includes both prehit (i.e., stealth, concealability, mobility, defense) and post-hit survivability (i.e., shock hardening, system redundancy , unsinkability).

A   discussion on the  importance  of a crew during damage control has this quote: “Surviva-bility or a submarine also depends on the subjective initiative of its crew. Under existing conditions, the crew’s efforts in repair work and peacetime maintenance can strengthen the submarine’s survivability.” Importantly, a survivable submarine design provides the crew with a framework of options to counter a casualty, but improper crew response or faulty equipment can quickly turn an otherwise survivable submarine into a crushed heap or metal.

A discussion or watertight compartments says: “To improve the submarine’s survivability, protect crewmen’s lives and save them from wreckage, several watertight compartments inside the pressure hull also have the function or lifesaving compartments . . . .  the lifesaving depth for the lifesaving compartment(s) depends on the pressure strength or its cross (transverse) bulkheads. This depth should be in accordance with the operating depth of the submarine. However, due to the limitations or structural weight and arrangement dimensions, the strength of the cross (transverse) bulkheads is usually less than that or the pressure hull.” Hence, multiple watertight compartments are installed into all PRC submarines.Several compartments  are designated as refuge compartments. Bulkhead weight and volume problems have apparently forced design compromises, such as test depth vice collapse depth rated bulkheads.

As for Underwater (Submerged) Unsinkability: “As with surfaced unsinkability, when a pressure bulkhead (compartment) and one or two of the adjacent main pressure ballast tanks (HBTs) are damaged and water enters, the submarine will still be able to dive, surface and navigate underwater. Modern submarines, however, may not be able to navigate underwater even when only one or the pressure compartments is damaged (flooded). There-fore, what we call the underwater unsinkability refers to the ability or the submarine, when one of the pressure compartments and the two main pressure ballast tanks adjacent to it are flooded, to use compressed air to blow water out of the undamaged main pressure ballast tanks to allow the submarine to surface automatically at a slight vertical angle. “In theory, submerged operations with flooding in one compartment is possible . . . but double-hull and multiple compartment submarines have a smaller degree of submerged unsinkability than optimum requirements might suggest”. PRC naval architects are not quite as optimistic about the submerged unsinkability features of their submarines as Soviet naval architects apparently are.

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