NAVSEA JOURNAL   May, 1975   SUSPENDED SUBMARINE SYSTEM   by   G. D. Campbell, SM4   Naval Underwater Systems Center   Newport, Rhode Island     The Naval Underwater Systems Center has been tasked by the Naval Sea Systems Command (PMS 402) to design, fabricate and operate a system capable of repeatedly and reliably lowering and raising a modified decommissioned submarine to a maximum depth of 300 feet for use as a target for exercise and inert loaded Mk 48 Mod 1 Torpedo runs. The ex-Menhaden (SS-377) has been designated for the program. Built by the Manitowoc Shipbuilding Company, the SS-377 was deployed in July 1945. Conversion to a Guppy IIA took place in 1953 and the submarine was deactivated in 1971. It is currently moored at the Naval Inactive Ship Maintenance Facility, San Diego, California. The suspension method being developed is a modification of the suspension system developed by NUSC (New London Laboratory) and used successfully to suspend the USS Trigger (SS-564) and other submarines in the mid-late sixties for the target characteristics measurements project (reference 1).   MK 48 Weapon Application   The primary objective of this program is to provide a real submarine target for the torpedo Mk 48 Mod 1 weapon system. Past evaluations have produced large quantities of useful data against artificial electronic targets, both moving and stationary such as the target Mk 17 and the mobile target Mk 27. There now exists a need for torpedo performance data against real targets, particularly against real submerged submarines. Safety considerations have prevented the gathering of this type of data, particularly in the areas of close-in dynamic and acoustic performance and warhead/exploder performance of the type that can be gained from "near-miss" and "hit" shots. An in-water run program will be generated to obtain these needed data. A portion of these runs will impact the submarine; at least five runs will be of this nature -- hardware considerations permitting. The torpedo runs will be conducted at the Naval Torpedo Station, Keyport, Washington, 3-D acoustic tracking ranges, Dabob Bay and Nanoose. Although past studies have indicated hull penetration is unlikely, for the first two impact runs, the submarine will be positioned in the shallowest portion of the Dabob range where the shallow water will enhance any possible required submarine salvage operations. After these initial tests for hull integrity, the remaining runs will take place at Nanoose where better acoustic conditions prevail. A live torpedo run (SINKEX) is being contemplated after completion of the inert torpedo run program, but only after other potential users of the submarine suspension system have had the opportunity to conduct any required tests and programs.   Suspension System   Figure 1 (not shown), an artist's concept of the submarine suspension system, shows the overall approach being used. Repeated use of this system requires that it be reliable and safe. Other requirements initially imposed on the system are simple and reliable operation and that it be recoverable from casualties, transportable and operable in moderate sea states (3 - 5) and survivable in higher sea states. The submarine will be suspended in a slightly negative buoyant (2k - 6k lb) condition from two long, thin cylindrical buoys attached fore and aft by 10-ton swivels and dynagrips fixing the cable ends to the submarine. The buoy shape is chosen to minimize the effects of sea states. Initial trim suspensions will be conducted by adjusting the amount of water in the fore and aft trim tanks and auxiliary tanks, the submarine having been already modified to permit this operation. Lowering and raising the submarine to a maximum depth of 300 feet will be accomplished by means of hydraulic cable pullers and cable take-up winches within each supporting buoy. These will be powered by a diesel powered hydraulic power package on board a nearby service ship. Quick disconnect hydraulic fittings are used to permit the service ship to depart during torpedo runs.   Communications between the service ship and the submarine will be via a radio link and it's own buoy housing a transceiver, power pack and connected to the submarine with an umbilical cable. The function of this subsystem is twofold. First and primarily it transmits submarine status signals (depth, pitch, compartment flooding, HP air, etc.) to a display console on the service ship. Second, the operator on the service ship can send a command to blow MBT and FBT tanks in the event of an emergency (hull rupture, etc.). An automatic blow is designed into the system in case of radio link communications loss for any reason such as control room flooding from a torpedo impact. This automatic blow feature can be inhibited by the operator when personnel are working in the vicinity of the submarine. The operator can also set in an adjustable delay to prevent blowing when communication is temporarily lost due to high sea states. A compartment flooding or detonation sensor will cause an automatic blow. An additional source of data will be from the suspension buoys themselves which will be calibrated in 1 ton stripes. The amount of submergence will indicate the weight of the buoy.   To enhance diver and camera inspection after each impact, the submarine will be painted a high visibility yellow. Each tank bulkhead will be painted with a black stripe and each tank number painted on the tank in large black letters to facilitate diver identification of the exact location of damage.   Trim System Modifications   Modifications and refurbishments to the submarine itself are covered in detail in reference 2. Rather than attempt to cover the details of all submarine modifications in this article, one particular example, that of adjusting the initial trim and buoyancy, will be discussed. The trim and buoyancy are attained by adjusting the amount of water in the auxiliary tanks and forward and after trim tanks until both suspension buoys have settled to a predetermined depth. Modifications permit this to be performed externally by divers with a nearby service ship equipped with a water pump and air compressor. Figure 2 (not shown) shows these modifications as a simplified schematic and the following two paragraphs describe the submarine modifications required to fill and empty the auxiliary and trim tanks.   The forward portion of the trim manifold will be removed, the trim line to negative will be blanked, and the flanged connections for the forward and after trim tanks will be reduced for the attachment of two new filling lines running through the hull. All valves on the remaining portion will be wired shut except auxiliary tanks, 1 and 2, effectively combining these two tanks. A third line for filling the auxiliary tanks will be attached and run along with the previous two new lines through the hull. External to the hull these three lines will terminate with valves and caps. The desired tank can be filled from the service ship by a diver connecting a water hose, opening the valve to the air pipe described below.   To empty the tanks, all tanks will be commoned at the 225 lb manifold and a single air line running through the hull alongside the three filling lines and terminating with a valve and cap. To do this, all valves on the 225 lb manifold will be locked shut except the four blow valves to the forward and after trim tanks and two auxiliary tanks. The service air hose connection valve will be removed and the previously mentioned pipeline running through the hull will be attached. Emptying the tanks is accomplished by a diver supplying 50 lb air to this line and opening the fill valve and cap to the tank being emptied.   Submarine Modifications   Additional submarine modifications will be discussed briefly. The high pressure air system and the 600 lb manifold will be modified to permit dockside charging and emergency blowing command through the radio link or by events such as flooding. The vent system modifications permit opening and closing the vents by divers connecting hydraulic lines externally while the submarine is on or near the surface. All normal fuel oil tanks will be free flooding with diver access permitted. The bow buoyancy tank will be free flooding. The forward and after torpedo rooms will have foam blocks installed to reduce the floodable volume. Depth sensors and flooding sensors will be installed and data transmitted to a submarine console (part of the radio link system). All remaining masts will be removed and the openings blanked. All unused hull penetrations will be blanked. Navigation lights will be installed according to the Rules of the Road for vessels under tow. The depth charge dogs will be attached and the strongbacks will be in place. Fairing plates will be installed over the after torpedo exit channels. All compartments will be checked for leakage. All batteries will be filled with fresh water after testing for chlorides. These previous items, while not all-inclusive nor given here in great detail, should be sufficient to convey the nature and magnitude of the modifications required for the ex-Menhaden.   Schedule   Current plans are to have the submarine suspension system operational during the second quarter of FY 1976 with the torpedo Mk 48 operations (except the SINKEX) complete in the third quarter of FY 1976. Since a suspended submarine system could have potential use for other ASW programs, the submarine could be made available to other programs prior to any consideration to a SINKEX.   References   1. NAVAL UNDERWATER SOUND LAB (U) Technical Memorandum 221-277-69, "Buoy Assisted Submarine Hovering System (U)," F.P Fessenden and F.J. Keltonic, 22 September 1969, UNCLASSIFIED.   2. SUPSHIPS 11th Naval District (U) Sketch No. 3081, "Shipboard Investigation/Concept and Engineering Recommendations for the ex-USS Menhaden (SS-377)" 27 September 1974, UNCLASSIFIED.     (The Above Information Courtesy of Ron Reeves, Retired HTC)   The USS Menhaden (SS-377) undergoing the "suspended submarine system" modifications at the Naval Ocean Systems Center drydock in San Diego, California.   (Image Courtesy of Don Morris, EN1(SS), Menhaden, 1966-69)   View of the USS Menhaden (SS-377) after all of the modifications described above were completed and she was towed to Keyport, Washington.   (Image Courtesy of Steve Bell, RM2(SS), Menhaden, 1963-65)