There are twenty-one historic submarines on display in the United States, more than any other single type of historic Naval vessel. Of those, sixteen are World War II submarines (including the captured German U-505), four are post-war diesel submarines and there is one nuclear submarine. A few of them are displayed on land, either on blocks or in landfill, most of them, however, are afloat. These historic submarines have much in common with regard to preservation problems. Some of these problems are common to all steel hulled historic ships, but many problems are unique to the design of submarines, both those built during WW II and after the war.

Submarines are often perceived as tough, durable vessels with thick hulls designed to stand up to the pressures of deep submergence. Although it is true that the pressure hull is much thicker than the hulls of other types of ships, there are portions of submarines that are designed to be free-flooding and are made of very light weight material. In order to understand the unique preservation problems facing World War II submarines, there must first be a basic understanding of their design and construction.


Problems that effect hull integrity are of primary concern. Most of the submarine floats on the outer hull which is made of 3/8" mild steel. The space behind this shell is divided into various tanks and the condition of these tanks directly effects the integrity of the outer shell. Originally the tanks, with the exception of the trim, negative, auxiliary and safety tanks, were accessible only through the flood ports located at the bottom of the tank. When the flood ports are blanked off with welded external plates during deactivation, covered access ports are usually installed on the tops of the tanks.

These tanks should be inspected to ensure that they are free of water or fuel and that the internal surfaces are well coated. It is also important that these tanks are sealed with proper gaskets at the access ports and that all vents, air salvage lines and blow lines are kept tightly closed. Tanks are potentially very dangerous to inspect, they can be fatal to the untrained. Proper safety procedures and the training and supervision of personnel is critical.

These tanks are saddle tanks that surround the bottom four-fifths of the pressure hull cylinder, the top of the pressure hull is not covered with an outer hull. The point at which the outer shell meets the pressure hull forms waterways (port and starboard) that run along the top of the pressure hull. They extend between the after bulkhead of the forward torpedo room to the forward bulkhead of the after torpedo room. Because the frames in this portion of the submarine are located on the outside of the pressure hull, they enter the saddle tanks at this point. Also, on some submarines, the vent risers and air salvage lines emerge from the waterways. These waterways are constantly full of water that comes down from the main deck from rain and wash downs. They should be kept free of debris and the scuppers cut through the frames should be kept open. A pump with a float type switch can be placed at the after end of the waterways to remove standing water as it accumulates. The waterways, the frames and piping in this area should be kept free of corrosion and should be well coated.

The biggest problem in treating the area under the superstructure is access to the waterways as they run aft of the conning tower. Forward of the conning tower access is relatively easy. The superstructure gradually decreases in height as you move aft making it a very cramped area. To further complicate matters this space also contains the large main air induction piping to the engine rooms and maneuvering room, the mufflers and exhaust piping for the diesel engines, air salvage piping and the ballast tank vent valves and risers.

To gain the access required to treat all of problem areas aboard Pampanito, five three foot square sections were cut out on each side of the after superstructure. These cut-outs allowed enough access to treat these areas, although the removal of the sand from blasting was still difficult. Once the areas were coated, the sections that were removed were welded back into place, the exterior surfaces of the weld seams were ground flush and both sides were coated.

The forward and after trim tanks are located at each end of the pressure hull. They are "hard" tanks of pressure hull thickness that are not open directly to sea, water ballast was pumped in and out of the tanks. The outer surface of the bulkhead at each end are, however, located in free-flooding areas. The forward end forms the after bulkhead of the free-flooding chain locker and surrounding void space. This means that part of the submarine's waterline, which is a problem area on all ships, is contained "inside" the vessel.

On Pampanito, the area just forward of the forward trim tank proved to be unexpectedly problematic. The chain locker flood ports had been blanked off at the bottom and the area was left open at the top. All of the anchor chain was still aboard and the locker was flooded from rain and wash down water. The chain was removed, stored shoreside and is considered to be an artifact which is an integral part of the submarine that will not be used for other purposes such as moorings or hand rails.

Over the years dirt and dust had settled in the void space around the chain locker and a dense corrosive mud formed at the bottom. Not only was the mud difficult to remove, there was literally tons of it, but it had caused pitting on the end of the pressure hull. The blanking plates were removed during Pampanito's first dry docking to allow this area to free flood and remain free of debris. The area was then sandblasted to white metal from eighteen inches above the waterline down to the bottom and coated per the underwater hull coating specifications. When Pampanito was dry docked again six years later this area was surveyed and found to be free of accumulated material and the coatings needed only minor repairs.

An option that was also considered was to keep the flood ports blanked off and seal the top of the void space and the chain locker to make them both water tight. This, however, would not only be expensive, but was an alteration that would effect the historic fabric of the vessel. Also, we had affected the trim of the boat slightly by removing the chain and did not want additional buoyancy forward that would have required adding lead ballast.

The after trim tank is similar in that the after bulkhead forms part of the free-flooding superstructure around the torpedo tubes. The tank itself was found to be in good condition, so all that had to be done was to prepare the internal surfaces of the superstructure and apply coatings. A problem in both these areas is access for personnel to work with sandblasting and painting equipment and the removal of sand.

Another potential problem that effects the watertight integrity of the hull are the through hull fittings and the flood ports for the ballast tanks. Pampanito's through-hull fittings were all blanked off when she was taken out of service at the end of WW II. Several of the blanks were removed, however, to fit her out as a Naval Reserve training platform. These included the sea chest for the after engine room, #2 sanitary tank blow and sea water flushing and the cooling water to and from the main air compressors. If they are to remain unblanked, it is very important that all open through-hull fittings are identified and the corresponding valves are located. The valves should be in good operating condition and they should be marked, remain closed and secured with a lock.

Torpedo tubes are also a potential problem. Most of the WW II submarines that are afloat sit about three feet above normal surface trim. This still leaves six of the ten tubes submerged and they should be thought of as twenty-one inch diameter through-hull fittings with no valve. Strongbacks are usually installed over the muzzle doors during deactivation to prevent them from being opened and there are interlocks to assure that both the breech and muzzle doors cannot be opened at the same time. However, many of the WW II submarines served as Naval Reserve training platforms and often the strongbacks were removed to allow for the firing of water slugs as a training exercise. The torpedo tubes, the gaskets around the inside of the doors and the interlocks should be regularly inspected. The tubes located below the waterline should never be opened before inspecting the tube for water.


The submerged portions of the superstructure that fair off the area around the muzzle doors of both groups of torpedo tubes have many problems. This area is constructed of a light-weight mild steel welded to light-weight frames and proved to be a difficult challenge when Pampanito was drydocked the first time. Once the area was sandblasted, many of the surfaces around the waterline area resembled fine lace and was perforated in several places. This required that frame sections be replaced as well as requiring several welded inserts. The torpedo shutter doors had been removed and stored aboard the submarine which allowed access to most of the problem areas, although some small areas were still very difficult to get at. Once repairs were made and the shutter doors and the superstructure were sandblasted and coated, the shutter doors were reinstalled to help shelter the interior surfaces.

This is an area that is closely monitored and evaluated during subsequent dry dockings. The idea of blanking off the shutter doors with welded plates has been discussed, but there are no plans to do so at this time. Blanking off these areas would create problems with added buoyancy, would limit future access and would alter the historic fabric. It would also present a problem for Pampanito's visitors who are very interested in how a submarine fires a torpedo and where it emerges from the boat. For these reasons we are very hesitant to blank off this unique feature of the submarine.

Pampanito's stem proved to be hollow and rusting through in three places. It was decided that it would be too expensive to replace the entire stem at that time. We also do not want to alter the historic fabric of the submarine, although this may have to be done at some time in the future. The problem areas were cropped out and inserts were welded in, but this left us with the problem of preparing and coating the interior surfaces. We were able to reach most of the stem's interior, but there was no way to monitor how thoroughly the coatings were applied. The stem of a vessel is a primary structural component and this is a problem that will have to be solved in the future.

The teak wood portions of the main deck, bridge and gun decks are a continual problem. Teak planks are through bolted to the superstructure frames with mild steel fasteners which are counter sunk flush with the deck. The recess around the bolt heads was then filled with pitch. Over time the pitch deteriorated and allowed water to seep down to the fasteners and waste them away. Because the planks are supported only at the frame where they are attached, there is a very weak point in between. When the plank is stepped on between the frames it can break at the frame. Several portions of the teak deck have been removed and the frames treated. New sections of teak that match the originals, including the unique scarf joints, were cut and bolted into place using higher grade fasteners. Instead of pitch, a clear epoxy was poured into the recess around the bolt heads. Once painted they match the original planks in appearance. Replacement of the rest of the teak deck is scheduled for the future.

The buoyancy tank which forms the bow of the submarine is made of the same light-weight material as the rest of the superstructure. It is open at the bottom of the tank through arch-shaped limber holes located above the forward torpedo tube shutters and it is vented through flapper valves located in the top of the tank. This tank requires regular maintenance in the harsh marine environment in which Pampanito is located. The tank is subjected to constant salt spray and is always open to the atmosphere, even when the vents and blow lines are secured. Problems do not have to go too long to become serious in this tank because of the light weight material from which it is constructed.


When Pampanito was taken out of service, the propellers were removed, as is the case with most of the other historic submarines. Steel "dunce caps" were installed over the threaded ends of the shafts and the nut that held the screw in place. When the submarine was in dry dock the caps were found to have developed leaks and the caps were carefully removed with a carbon arc. The taper of the shafts and the nut were packed with heavy marine grease and the original caps were then welded back into place, covered with several layers of fiberglass and coated per the underwater hull specifications.

Periscopes and the pressure-proof binoculars on both target bearing transmitters were charged with dry nitrogen and purged to remove moisture. They should be checked regularly and purged when necessary to keep moisture from building up.


Submarines are usually thought of as being virtually indestructible because of their thick pressure hulls. However, most of the vessel that is in contact with the water is the outer hull which is the same thickness as most other steel-hulled ships. There are also areas that are free-flooding, made of light weight material, that are extremely vulnerable. Submarines also have many unique features such as submerged torpedo tubes and open flood ports at the keel that can cause long term problems. Access for personnel to evaluate and work on problem areas is a constant problem. Submarines are indeed tough, durable vessels, but because of their design there are many problems that are unique. An understanding of these problems is essential to long range planning and the preservation measures that are taken.


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Version 2.00, 11 Sep 2006