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This article needs to be updated. The reason given is: which type designations are still in use by the US Navy and which, if any, vessels are still in service. Please help update this article to reflect recent events or newly available information.(April 2024)
A floating drydock is a type of ship repair facility that has been used since at least the early 19th century. It was adopted for widespread use by the US Navy in the early 20th century as a critical element in the Service Force that was being conceived to provide support for the fleet in an expected war with Japan. A floating drydock is generally a trough-shaped construction larger than a ship which incorporates ballast tanks under its floor and in its sidewalls. When a ship needs repair the ballast tanks are flooded, lowering the structure into the water to a depth at which its floor is deeper underwater than the bottom of the ship to be repaired. The ship is then maneuvered into a position between the sidewalls and over the floor of the dock, at which point the tanks are pumped out again, lifting the floor of the structure back out of the water, with the ship perched on a series of supports carefully positioned to match the contour of its underside. This leaves the vessel perched securely out of the water so that work on its underside can be undertaken.
All ships, but particularly naval vessels in continuous use during wartime, need periodic maintenance (such as cleaning of barnacles and seaweed off of hulls, and repainting) and repairs (of battle damage, or of damage resulting from collisions, groundings, or other types of accident) below the waterline. Such work often requires dry docking. Since before World War I American plans for a Pacific war had called for a movement across the central Pacific by amphibious forces, who would capture strategically placed territories and establish advance bases there. Ultimately, when this string of bases reached points close enough to Japanese home territory, bombing aircraft would be sent to the farthest forward of the bases and used to prosecute war against the Japanese home islands, a task that would require significant logistical support in and of itself. This was an unprecedented type of warfare, because of the lengths of supply lines dictated by the distances involved, and the quantities of supplies that would be necessary to support such a massive offensive so far from home. Ships involved in the advance would require maintenance and repairs. It was recognized at an early date that, to minimize the need to send ships in need of such servicing all the way back to North America, it would make sense to equip these newly established advance bases with the most comprehensive repair facilities that could be set up in faraway locations in short order. The provision of dry docks for these faraway bases was going to be necessary, and in 1920 the Navy began to develop a number of types of floating dry dock, of various sizes, that would be suitable for towing across long distances. Construction of such drydocks was begun on a large scale in 1940.
At the start of World War II, the US Navy had only three steel floating dry docks:
YFD-2, built in 1901, was stationed at Pearl Harbor. The destroyer USS Shaw was being repaired in the dock on 7 December 1941 during the attack on the harbor. Both YFD-2 and USS Shaw were repaired, after being hit and damaged in the attack.[1]
USS Dewey, built in 1905, had been deployed to the Philippines through most of its career. It was scuttled at Mariveles to prevent its capture by the Japanese. In 1942 Japan raised the Dewey, but it was resunk by US forces.
ARD-1, built in 1933, was also at Pearl Harbor. It was a self-sustaining mobile dry dock.
By the end of the war the Navy had either built or acquired from private owners a total of 155 docks of varying types and sizes. Between 1 October 1944 and 17 October 1945, 7,000 ships were repaired in these docks.
The newly built floating dry docks had lift capacities ranging between 400 and 100,000 tons. While most floating drydocks were made of steel, considerable numbers were made of concrete or timber instead. Timber floating dry docks had lift capacities of anywhere from 400 to 20,000 tons. They were not meant to be towed across the open ocean and were not given a US Navy class designation.[2][3]
Docks come in different sizes to accommodate ships of different sizes; while most, including the earliest examples, are built as a single unit, the largest, designed to accommodate the largest ships, are too large to be moved across open ocean as a single unit, and are therefore built in sections which can be transported individually and assembled at their work site.
Most floating drydocks had no propulsion system of their own, and therefore had to be towed to their destinations. Most incorporated power stations, ballastpumps, repair shops, and machine shops, and many had cranes.[4][3] Most incorporated quarters, mess halls, and other accommodations for their own crews, to make them as self-sustaining as possible, and thereby minimize the need for support vessels or additional facilities ashore. Some also had accommodations for crews of the ship under repair, although most of the time the crew of the damaged ship remained on board their own ship while repairs were done.
Myriad designations were applied to the different types of drydock built under this program. Post-war, to rationalize the system of designations, most drydocks were redesignated as Auxiliary Floating Drydocks, with Big (AFDBs), Medium (AFDMs), and Light (or Little; AFDLs) subsets. A few other designations (two Medium Auxiliary Repair Docks [ARDMs], of post-war origin, in active service, and several Auxiliary Repair Docks [ARDs] and Auxiliary Repair Docks, Concrete [ARDCs], sold into private or foreign service and possibly available for U. S. Navy use) are also still in use, for docks that do not quite meet the parameters of any of the AFD categories.
Auxiliary Floating Docks, Big (AFDBs) (Previously Advanced Base Sectional Docks (ABSDs))
The largest floating drydocks built for the Navy during World War II were two classes initially categorized as Advanced Base Sectional Docks (ABSDs). These docks were built in multiple sections for towing to the locations where they would be used; the sections were then assembled, side by side, to produce a single structure capable of accommodating ships nearly 1,000 feet long. Post-war the ABSDs were redesignated as Auxiliary Floating Dry Docks, Big (AFDBs).
The larger of the two classes, of which three (ABSD-1 through ABSD-3) were built, were made up of ten individual sections, oval-shaped pontoons that measured 256 feet (78 m) in length (from the tip of one roughly semicircular end to the other) and 80 feet (24.4 m) in width. The pontoons were 28 feet (8.5 m) thick (deep), with plating roughly 5 1/2 inches (14 cm) thick forming the upper and lower surfaces. Each pontoon incorporated 12 flotation tanks within its structure, flanking a 36-foot (11-m) wide, 80-foot (24.3-m) long vacant space, which contained accommodations for enlisted personnel on an upper floor, and storage compartments beneath, running widthwise across its center. Each pontoon supported two sidewalls, 80 feet (24.3 m) long (spanning the width of the pontoon), 55 feet (16.7 m) high, and 20 feet (6.1 m) thick. The sidewalls were spaced 137 feet, 6 inches (42 m) apart (inner surface to inner surface), with their outer edges at roughly the points where the curves of the semicircular ends began. The sidewalls could be folded down, to lie across the center of the pontoon, and then the whole segment could be towed, with the rounded ends fore and aft, at a reasonable speed. Fittings for anti-aircraft guns were located on the outer sides of the walls, so that such weapons could be mounted on top while the section was being towed. The crew generally travelled aboard the dock sections.
Upon reaching the destination the walls were raised and the pontoons joined together, side by side, with the semicircular ends of each pontoon projecting out beyond the walls, adding to lateral stability. Assembled, the core of the structure was 827 feet (252 m) long (80 feet [24 m] for each pontoon, with 3-foot [1-m] gaps left between each unit and the one next to it). Sources report that a 50-foot (15-m) long section of some sort was appended to each end of the assembled structure, giving an overall 927-foot (283-m) length to the structure; no readily available source gives a clear idea of what these extensions amounted to, although photos suggest that they may have been shelf-like structures that did not extend down even to the water's surface, much less supply any buoyancy. Flooding of ballast tanks incorporated into the pontoons could lower the deck to a depth of some 49 feet (15 m) below surface, so that a ship to be worked on could be maneuvered into a position over the pontoons and between the walls, with the ballast tanks then being pumped out, raising the pontoons back to the surface and leaving the ship perched atop carefully arrayed blocks set up on the pontoons' upper surfaces.
The smaller class of ABSD, of which four (ABSD 4 through 7) were built, was structured similarly to the larger class, but incorporated only seven pontoons, each 240 feet (73 m) long and 100 feet (30.5 m) wide, with 49-foot (15-m) high, 18-foot (5.5-m) thick sidewalls spaced 120 feet (36.5 m) apart (internal surface to internal surface). The decks of these structures could be submerged to a depth of approximately 44 feet (13.4 m) below surface. Overall length of the assembled dock was approximately 820 feet (250 m).
AFDBs had crews of 600 to 1,000 men. They were equipped with fresh-water distilling plants and, perched on a rail atop one of the sidewalls, a 15-ton-capacity crane with an 85-foot (26-m) reach. To pump water from the ballast tanks, on each section there were two 24-inch (61cm) discharge pumps, each of which could pump 15,000 US gallons (57,000L) per minute, powered by a steam plant. For electricity, there were two 350-kw diesel AC generators on each section, producing 3-phase 60-cycle power at 440 volts. Each section could store 65,000 US gallons (250,000L) of fuel oil to supply the ships under repair. Crews lived in barracks ships, called APLs, that docked next to the AFDB, as didtwo or more support bargess.[2][6][3][7]
More than half of all floating drydocks built for the United States Navy were initially classified as Yard Floating Docks (YFDs). This term was a catch-all, and did not describe any particular type of dock: docks with lifting capacities ranging from 400 to 20,000 tons, made of metal, concrete, or wood, were all designated under this category. Post-war, however, 14 large units with relatively uniform characteristics were redesignated as Auxiliary Floating Docks, Medium (AFDM). These docks were all of metal construction, and were constructed in three sections, a large central section with shorter sections appended to each end. They displace between 6,800 and 8,000 tons and measure between 528 and 622ft (161 and 190m) in length. Their structures incorporate 16 ballast tanks, and have lift capacities of c.18,000 tons, sufficient to lift a cruiser or nuclear submarine. They are equipped with two 7+1⁄2-ton cranes, mounted on the upper edges of the two side walls. In wartime they were armed with two 40mm and four 20mm guns.[2][16][3][17] Unlike most YFDs, these docks were relatively transportable.
The term Auxiliary Floating Dock (AFD) was initially applied to small, single-unit docks, 200ft (61m) long, with a beam of 64ft (20m) and a draft of 14.5ft (4.4m) over the blocks when submerged. Open at both ends, they were capable of lifting vessels displacing no more than 1000 tons, such as minesweepers, patrol vessels, and yard utility vessels. When slightly larger vessels began to be built (notably destroyer-escorts), it was decided to take five of the AFDs (AFD-7, AFD-12, AFD-22, AFD-23, and AFD-26) and lengthen them by 88 feet (26.8 m), raising displacement to 1,200 tons and lifting capacity to 1,900 tons. These five docks became known as Auxiliary Floating Docks, Lengthened (AFDLs). All these vessels were self-contained, carrying their own power generating equipment, and were assigned crews of 60.
Somewhat confusingly, all AFDs and AFDLs were reclassified as AFDLs, now meaning "Auxiliary Floating Docks, Little" (AFDL), in 1946.[2][28][29]
Auxiliary Repair Docks (ARDs) are eminently towable structures, with enclosed, ship-like bows and rudders at the stern to improve their towing characteristics. Their sterns are open, to allow vessels to be worked on to be taken aboard. They measure (external dimensions, with some variance between different subclasses) 483ft (147m) in length and 71ft (22m) in beam, displace 4,800 tons, and draw 5ft (1.5m) when the ballast tanks are empty; their usable (internal) space measures 413 feet by 49 feet 4 inches, and they can be submerged to a depth of 21 feet above the top of the blocks on which ships being serviced are perched. With a nominal lifting capacity of 3,500 tons they were, during the war, appropriate for use in repairing destroyers, submarines, Landing Ship, Tanks (LSTs), and other small- to medium-sized vessels. The docks were armed with two single Oerlikon 20 mm cannons for anti-aircraft work. They have two five-ton-capacity cranes perched atop their side walls. A stowage barge is assigned as an auxiliary to the dock. The crew consists of 6 officers and 125 enlisted men. All ARDs were built by Pacific Bridge Company of Alameda, California.[2][3][58]
USSARD-1 Displacement of 2,200 tons. Built in 1933. Only one in class.[59]
Three Auxiliary Repair Docks (ARDs) built during World War II were rebuilt post-war, being lengthened by 50 feet (15 m) and having their sidewalls raised slightly in height. These were reclassified as Medium Auxiliary Repair Dry Docks (ARDMs). Two additional docks in this category were built in 1977 and 1983, respectively.
ARDC-13, An Auxiliary Repair Dock, ConcreteAuxiliary Repair Dock, Concrete under tow
Auxiliary Repair Docks, Concrete were mobile (towable) dry docks made of concrete, due to the shortage of steel during World War II. Somewhat smaller than metal ARDs, ARDCs measured 389ft (119m) in length, 84ft (26m) in width, and 40ft (12m) in depth. ARDCs had crews of five officers and 84 enlisted men. The first ARDC had a built-in diesel power supply, while the remainder relied on outside power sources. All were equipped with a 5-ton crane with a 42ft (13m) reach. Eight were built at Wilmington, North Carolina, and five at San Pedro in Los Angeles, California.[92][93][94][3]
ARDC 1 – Changed to AFDL-34. Sold to Taiwan in 1959 Han Jih.
ARDC 2 – Changed to AFDL-35. Scrapped in 1974.
ARDC 3 – Changed to AFDL-36. Sold to Taiwan in 1947 Hay Tan. Scuttled in 2000.[95]
ARDC 4 – Changed to AFDL-37. Scrapped in 1981.
ARDC 5 – Changed to AFDL-38. Placed out of service, date unknown. Final Disposition, transferred to San Francisco Maritime National Historical Park and leased to Bay Ship and Yacht shipyard at Alameda, CA.[96]
ARDC 6 – Changed to AFDL-39. Sold to Brazil in 1980 Cidade de Natal.
ARDC 7 – Changed to AFDL-40. Sold to the Philippines in 1990.
ARDC 8 – Changed to AFDL-41. Sold in 1983 to North Florida Shipyard[97]
ARDC 9 – Changed to AFDL-42. Sold to Hurley Marine Works in 1945. Scrapped in 1975.
ARDC 10 – Changed to AFDL-43. Scrapped in 1979.[98]
ARDC 11 – Changed to AFDL-44. Sold to the Philippines in 1969.[99]
ARDC 12 – Changed to AFDL-45. Sold to Todd Seattle 1945. Sold 1981 to Puglia Engineering.
ARDC-13 – Changed to AFDL-46. Destroyed at Bikini in 1946.[100]
YFD-2 The first Yard Floating Dock built in 1901, arriving Pearl Harbor 23 Oct. 1940 from New Orleans Naval Yard
The designation "Yard Floating Dock" (YFD) was used for floating docks of a variety of sizes and types, built mostly for harbor or shipyard use. YFDs normally had little to no crew space and were serviced from shore. Some Auxiliary Repair Docks were converted to YFDs. Types of YFDs included: 400-ton concrete docks; 1,000-ton, 3,000-ton and 5,000-ton wooden docks; wooden sectional docks with 7,000 to 20,000 ton lifting capacities; and three-piece self-docking steel sectional docks (whose individual sections could be docked for repairs within a shortened dock made from the rest) with 14,000 to 18,000 ton lifting capacities. Fourteen YFDs were redesignated as Auxiliary Floating Docks, Medium (see above) after World War II.[101][102][3]
USSABSD-3 at Guam ca. September 1945 repairing USS Pennsylvania (BB-38), to the rear right of ABSD-3 is the land base that supported the ABSD-6 and ABSD-3 crews
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USS Pennsylvania (ACR-4) in dry dock Dewey, c. 1906–1907
USS Maryland (ACR-8) in dry dock Dewey, c. 1907
USS Chauncey (DD-3) in dry dock Dewey, c. 1910
USS Chauncey (DD-3) in dry dock Dewey, stern view, c. 1910
US Navy submarines in dry dock Dewey, c. 1912
US Navy submarines in dry dock Dewey, c. 1912
USS Galveston (CL-19) in dry dock Dewey, c. 1916
Aerial view of dry dock Dewey with USS Jason (AV-2) nearby, October 1928
Aerial view of USS Jason (AV-2) in dry dock Dewey, 8 March 1932
Side view of USS Jason (AV-2) in dry dock Dewey, 9 March 1932
USS Octans (AF-26) in YFD-18 at San Francisco on 15 June 1943
Cruiser Columbia (CL-56) docked in Artisan (ABSD-1) at Espiritu Santo in January 1944
Columbia docked in Artisan ABSD-1 at Espiritu Santo in January 1944
One Advance Base Sectional Dock (ABSD) section under tow with float wings up in 1944
AFDB-1 with USS West Virginia (BB-48) high and dry in the dock November 1944[106]
USS Iowa (BB-61) floating in dry dock at Manus Island, Admiralty Islands, 28 December 1944
USS LST-646 and USS LST-662 in ABSD-6, in Apra Harbor, Guam, 29 May 1945
USS Makin Island (CVE-93) halfway into USS ABSD-6, at Guam, 8 June 1945
USS AFDB-2 at Seeadler Harbor in 1945
ABSD-6''s Section D and one crane under tow to Guam. Pontoons are folded down to reduce wind resistance and lower center of gravity
USS ABSD-6 being assembled at Apra Harbor, Guam in 1945
ABSD-3 repairing small ships (likely Admirable-class minesweepers or PCE-842-class patrol craft) at the same time at Guam in 1945
USS ABSD-3 at Guam ca. September 1945 repairing USS Pennsylvania (BB-38), to the rear right of ABSD-3 is the land base that supported the ABSD-6 and ABSD-3 crews
USS Abraham Lincoln (SSBN-602) in USS AFDB-7 at Holy Loch, Scotland, on 19 March 1963
Los Alamos (AFDB-7) at Holy Loch, Scotland, on 1 December 1985
Official crest of Arco (ARDM-5)
USS Asheville (SSN-758) enters the floating dry dock of Arco (ARDM-5) for scheduled maintenance at Naval Base Point Loma, California, on 25 April 2007_in_Drydock_Dewey.jpg)
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This article incorporates public domain material from Artisan (AFDB 1) sections A, G, H, I, & J, Section E, Section F, IX-534 (ex ABSD-1 section B), IX-525 (ex ABSD-1 section C), and IX-521 (ex ABSD-1 section D) at the Naval Vessel Register.