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I recently got the opportunity to visit the Pearl Harbor Memorial. In the informational video that they show guests, they mentioned a detail I found fascinating: most of the ships sunk in the Japanese surprise attack, including several of the massive battleships, ended up being raised and put back into service in the war.

That made me wonder. How did they go about re-floating a ship as enormous as a battleship, with a sinking hole in it, with 1940s technology? What was the process like for doing that?

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    Google returns plenty of results. – Steve Bird Apr 26 '18 at 7:33
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    I vaguely remember from my visit 30 years ago that many of the ships purposely tried to run themselves aground so that salvage/repair would be easier if they were hit. – T.E.D. Apr 26 '18 at 15:00
  • A very good book which contains a first-hand account: Descent into Darkness: Pearl Harbor 1941: A Navy Diver's Memoir. – John Coleman Apr 27 '18 at 1:14
  • I'm voting to close this question as off-topic because how to salvage ships can easily be found online. – Jos May 2 '18 at 7:33
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First, it helps to understand that the Pearl Harbor anchorage is fairly shallow. The battleships weren't completely underwater. Their superstructures and main gun turrets were still visible, and in some cases, the upper deck was out of water. This was one of the flaws of the Pearl Harbor attack... had the ships been attacked in open water, they would have been completely lost in deep water.

The US Navy documented the salvage on this site. Here's a quick summary:

USS Nevada was the first to be salvaged, as it didn't actually sink. Nevada was able to get under way during the attack, and was run aground when flooding from a torpedo hit threatened to sink it. Divers plugged the one torpedo hole and several bomb holes, water pumped out, and Nevada was refloated with a month. In the process, several people died from high concentrations of hydrogen sulfide gas that had accumulated in the hull, leading to stringent anti-gas measures being taken for the rest of the salvage effort.

USS California had a lot more holes in it, requiring a cofferdam to be built around portions of the hull to get the damaged area above water for repair. Some of the superstructure and the main gun turrets were removed to lighten the ship. California, along with West Virginia, were returned to service by 1944.

Less damaged were USS Pennsylvania, Maryland, and Tennessee, as they were on the inside row (the battleships being docked in two rows) and thus not subject to torpedo attack, only bomb attack. They were refitted, upgraded and returned to service by 1943.

USS Oklahoma and USS Utah had capsized, rolled over, due to one side of the ship being flooded from torpedo hits. They were righted by parbuckling, a procedure used to right the Costa Concordia during its salvage, where cables are attached to platforms built on the hull and then the hull was rolled back upright. These two ships, along with USS Arizona, were too badly damaged to be returned to service, and all three remain in Pearl Harbor today. Their guns were removed and transferred to harbor defense or new construction. Their salvage was more to remove the bodies trapped in the hull than anything, except for Arizona, whose casualties remain in the hull to this day.

Overall, the salvage of the Pearl Harbor battleships was one of the more impressive engineering feats of the war. This was as much national pride as anything - by the time the last battleship had been refloated, both sides in the war recognized that the aircraft carrier was now the most prominent naval weapon in the war.

Unless the aircraft carriers are sent in the wrong direction...

In a twist of irony, salvaged Pearl Harbor battleships California, Tennessee, Maryland, Pennsylvania, and West Virginia spearheaded the last battleship on battleship action in history. They were attached to Admiral Jesse Oldendorf's Seventh Fleet when it met Admiral Nishimura's Southern Force in the Battle of Surigao Strait, 25 October 1944, as part of the Leyte Gulf action. Nishimura's fleet was roundly defeated by the 'ghost ships' of Pearl Harbor, with both of his battleships being sunk.

This action played out as pure ship on ship as Halsey had sent all of his carriers after Ozawa's decoy carriers... which had almost no aircraft or pilots.

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In the case of the USS California, the ship had been holed in the hull by two torpedoes and a bomb. The salvage teams worked to install floatation devices to raise the area holed by the Japanese above the waterline of the ship. As salvage efforts continues they discovered that, discounting the two torpedo holes, the ship was relatively water tight meaning the ship did not need to be patched before having the flooded compartments pumped clear and the ship re-floated.

For the USS West Virginia, which was struck by around 8 torpedoes and several bombs, as the damage was much more extensive the hull required a great deal of patching before it could be re-floated.

In the case of both ships, in order for the re-floating to occur, they had to remove a great deal of weight by removing armaments and ammunition, remaining fuel oil and parts of the superstructure.

After re-floating, the ships underwent various repairs in dry dock at Pearl Harbour, after which they travelled to Puget Sound Navy Yard for more extensive repairs before returning to active service.

Information on the salvage of USS Navada, USS California, USS West Virginia, USS Oklahoma, USS Utah, USS Shaw, USS Downes and USS Cassin can be found on history.navy.mil.

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    It might be just me, but I kind of read the question as: how would one re-float a boat in the 1940s? Expanding a little on that would make this nice answer a great answer. – Denis de Bernardy Apr 26 '18 at 9:14
  • @DenisdeBernardy: See livescience.com/… The basic idea is to attach something to the ship, usually by sinking it, then pumping the water out. "Camels" were used to lift ships over the bar in the days of Commodore Perry on Lake Erie, in 1813: historynet.com/oliver-hazard-perry-and-the-frontier-fleet.htm – Peter Diehr Apr 26 '18 at 15:05
  • "The salvage teams worked to install floatation devices to raise the area holed by the Japanese above the waterline of the ship." According to the US Navy they didn't install flotation devices but instead built cofferdams. These effectively raised the waterline, but did not raise the ship. – Schwern Apr 26 '18 at 19:56
  • @Schwern: Did you mean lowered the waterline? – Sean Apr 29 '18 at 20:57
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On the general question how to they refloat sunken battleships, there is a wonderful book: Joseph N. Gores, Marine salvage, David &Charles Newton Abbot, 1971. In particular, it describes how the whole German fleet sunk in 1919 (11 battleships, 5 battle cruisers, 74 ships in total) were salvaged in 1924. So by 1941 there was a well-developed technology.

It is difficult to describe all these techniques in few sentences, this involved a lot of clever inventions. First they lifted smaller ships (destroyers) simply with winches placed on barges. The ropes had to be set under the sunken ship, so there was a lot of work for divers (they drilled tunnels in the sea bottom under the hull!). Then they lifted cruisers. To lift a battleship, they sunk several smaller ships next to it, properly prepared, that is hermetically sealed, more or less, and secured them to the sunken battleship. Then they pumped air from the surface to these smaller ships, to lift the battleship. In certain cases, when a battleship was laying upside down, it was possible to close the major holes in it, and pump air to it, to displace water. A complicated combination of these and other techniques was used in each case, depending on the battleship condition and position on the bottom. All this required enormous amount of work of divers. Fortunately the place was not too deep.

Of course they did all this only to salvage the metal, but they were able to tow the refloated battleships for long distance. (One of them was towed upside down!). So repairing the battleships to a usable condition was of course another engineering feat. But those in Pearl Harbor also did not do this for the first time. The British were able to restore two battleships sunk by the Italians in Alexandria before that. This is also described in the same book. I do not know why this (British) author did not describe in detail what happened in Pearl harbor.

The difficulties in general strongly increase with depth. Most of these operations were performed in shallow harbors. So American partially successful attempt to lift a Soviet submarine from 5km depth(!) in 1974 remains unmatched. See "Project Azorian" on Wikipedia, which also has references (including a youtube movie).

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