SUBMARINE EXTERNAL ROTARY RACK WEAPONS SYSTEM

Mr. Henry is a League member and is Treasure of the Capital Chapter. He is a naval architect and retired from Naval Sea Systems Command in 1999 after 35 years of working in early-stage submarine design and research and development management. His last position was as Head of Submarine Preliminary Design and as Principal Naval Architect for the Virginia class.

A Submarine External Weapons Delivery System, hereinafter referred to as the rotary rack system, was developed in 1969-70 under the sponsorship of the U.S. Navy’s SSN Continuing Concept Formulation (SSN CONFORM) Program. The basic concept of the rotary rack system is a movable carriage mounted on and revolving around the pressure hull in a double hull section of a submarine. Weapons are stored within the rotary rack structure and move with the rack to appropriate launch locations. [The “Magnum” revolving rack concept, described by Harold Armstrong in the January 1999 edition of THE SUBMARINE REVIEW, has many similarities to the rotary rack system.]

Concepts were developed for rotary rack installation in a submarine’s bow or amidships, i.e., around bottlenose or wasp waist pressure hull sections, in an otherwise single hull ship configuration. The figure shows a notional bow installation. A bow system would replace the contemporary SSN torpedo room and its angled torpedo tubes. An amidships system is independent of the torpedo room, which could be retained or eliminated based on other criteria.

Torpedoes are stored wet and at ambient sea pressure. To prevent corrosion, each weapon is packaged in a flexible waterproof container (e.g., a plastic bag) containing a non-corrosive fluid. Torpedoes, which tend to be denser than water, are launched near the ship’s keel using a trapeze-like mechanism to move the weapon from its stowed position between the hulls into the free stream and to impart an initial forward velocity, a requirement for some torpedoes. Torpedo launch is feasible from both bow and amidships launchers.

Cruise missiles are stored dry in buoyant capsules. Launch is accomplished by releasing the buoyant capsules at topside launch positions. The capsules float to the surface where the missile is ejected. similar to the later developed Encapsulated HARPOON system. Missile launch is feasible from bow and amidships launchers. However. there is risk that the sail may impact bow launched buoyant capsules and the amidships scheme is preferred.

Both missiles and torpedoes are loaded at a topside launch position. Shutter doors provide a smooth hull surface except during weapon launch.

(More recent submarine external weapons concepts typically place weapons in pressure proof canisters to maintain an appropriate environment for the weapon. To launch a weapon. canister pressure is equalized with the surrounding ocean, an end closure opens, and the weapon is impulsed into the free stream (e.g., by means of a gas generator or catapult). This approach was considered during the course of rotary rack development but was not included for two reasons. First, it replaced a submarine’s weapon launchers (four torpedo tubes and two impulse devices) with a number equal to the number of weapons. Second, it requires firing the weapon forward or aft, either of which adversely impacts the geometric configuration of what otherwise were single-hull, body of-revolution ships, causing ship size, drag and cost to increase.]

A number of alternative concepts were developed during the 1969-70 study. The principal differences between Electric Boat and Lockheed developed rotary rack concepts are summarized below, as applied to torpedo stowage and launch.

The primary areas of concern for rotary rack system weapons, loading, handling, storage and launch were as follows.

• Environment: shock, corrosion, marine growth, cyclic fatigue on weapon pressure boundary components and seals, etc.
• Stowage: the rotating rack places weapons in non-upright positions (unless the system can independently rotate the weapons, keeping them upright, as the rack rotates – an undesirable added complexity), lack of accessibility for weapon maintenance, etc.
• Communication and power: existing methods for transferring data and power to the weapon could not be used.
• Launch: existing methods for external launch were very noisy, problems associated with launching most likely could not be corrected until the submarine returned to port, the location of launch ways severely limits launch speeds, and the potential ship impact with a dud weapon needed to be resolved. Buoyant missile capsules cannot be launched when the submarine is surfaced.
• Fabrication, operation and maintenance: external rack poses significant problems related to fabrication, operation throughout the submerged operating envelope, and maintenance over a ship’s life cycle.
• Redundancy: none-a single casualty to the rotary rack would probably abort a mission.

In addition to system concept design efforts, the Submarine External Weapons Delivery System project sponsored selective technology development to validate the concept. The more notable tasks included:

• Model tests: conducted by the Naval Ship R&D Center in the high speed model basin at Carderock, demonstrated that denser than water weapons could be successfully launched near the keel at high submarine speeds.
• Model tests: conducted by Lockheed in the Lockheed Underwater Missile Facility (LUMP) at Sunnyvale, demonstrated that buoyant capsules could be successfully launched from topside.
• Compatibility studies: conducted by the Naval Underwater Weapons Research and Engineering Station, demonstrated the compatibility of the Mk 48 torpedo and the Mk 28 missile (SUBROC) with external storage and launch.

The current torpedo room occupies valuable space inside the pressure hull and building and installing weapon stowage structure, torpedo tubes, the shipping system, etc., utilizing expensive materials and with many critical alignments, is very costly. However, this configuration provides a very dense weapon stowage scheme with heavy weights low in the submarine.

A rotary rack scheme, in lieu of a torpedo room, eliminates the torpedo room and weapon stowage structure, the torpedo tubes, the weapon shipping trunk and system (including the need for center line cutouts on the platform decks), the weapon ejection system (ejection pumps, firing valves, impulse tank), many large pressure hull penetrations, and also reduces manning requirements. However, it has its own significant implications on total submarine design. Some of the more important torpedo room versus external rotary rack tradeoffs are discussed below.

• Double hull submarines tend to be larger, slower, and more expensive than single hull submarines. This also pertains to partial double hull submarines.
• The rotary rack and all of its associated component weights are higher in the submarine. In a stability limited design, this would require additional stability lead and, perhaps, cause the ship to increase in size.
• The external weapons space between the pressure hull and outer hull cannot be used as main ballast tankage due to the large topside openings for weapon shipping and missile launch. The volume of this free flooded space wilt be approximately the same as the torpedo room volume and the overall ship will be larger unless the torpedo room is removed.

Removing the torpedo room can be accomplished only if the submarine does not require the buoyancy provided by the torpedo room volume to achieve neutral buoyancy. While the weights associated with the torpedo room weapon stowage structure, torpedo tubes, weapon shipping trunk, and weapon ejection system are eliminated, the rotary rack system adds the weight of the rack, additional outer hull structure, large shutter doors, operating mechanisms, etc.

• A torpedo room provides space for alternative purposes, e.g., SEAL teams and UUVs. [This is particularly true in the Virginia class with its reconfigurable torpedo room.] Even if all weapons are external, some alternative uses require one or more torpedo tube-like features to transfer payloads from within the submarine to the water column and, perhaps, to also retrieve payloads.

While considerable engineering development efforts would have been required to field an operating rotary rack submarine external weapon delivery system, the design and advanced development efforts conducted in 1969-70 demonstrated the fundamental feasibility of such a system. However, the rotary rack system was not included as a candidate weapon delivery system in subsequent submarine design concepts due to what were then considered overwhelming system and total ship disadvantages. Perhaps today’s innovative submarine designers, applying advanced technologies. will overcome the hurdles encountered during the past thirty years and create new and improved submarine weapon delivery system.

Most of the organizations involved in the 1969-70 Submarine External Weapons Delivery System development have changed names due to reorganizations and mergers. The sponsoring SSN Continuing Concept Formulation Program (no longer existing) was managed by PMS 393 (now PMS 392) in the Naval Ship Systems Command (NAVSHJPS, now part of NAVSEA). Development efforts were primarily performed by the Naval Ship Engineering Center (NAVSEC, now part of NAVSEA), the Naval Ordnance Systems Command (NAVORD, now pan of NAVSEA), the Naval Ship Research and Development Center (NSRDC, now NSWCCD), the Naval Underwater Weapons Research and Engineering Station (NUWS or NUWRES, later NUSC, now NUWC), General Dynamics/Electric Boat Division (GD/EB) and Lockheed Missiles &: Space Company (IMSC, now Lockheed Manin Missiles & Space).