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A dock landing ship (also called landing ship, dock or LSD) is an amphibious warfare ship with a well dock to transport and launch landing craft and amphibious vehicles. Some ships with well decks, such as the Soviet Ivan Rogov class, also have bow doors to enable them to deliver vehicles directly onto a beach (like a Landing Ship, Tank). Modern dock landing ships also operate helicopters.
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A ship with a well deck (docking well) can transfer cargo to landing craft in rougher seas than a ship that has to use cranes or a stern ramp. The US Navy hull classification symbol for a ship with a well deck depends on its facilities for aircraft - a (modern) LSD has a helicopter deck, a LPD also has a hangar, and a LHD or LHA has a full-length flight deck.
History
The LSD (US Navy hull classification for landing ship, dock) came as a result of a British requirement during the Second World War for a vessel that could carry large landing craft across the seas at speed.
Predecessor of all modern LSDs is the Japanese amphibious assault ship Shinshū Maru of the Imperial Japanese Navy, which could launch its infantry landing craft using an internal rail system and a stern ramp. She entered service in 1935 and saw combat in China and during the initial phase of Japanese offenses during 1942.
The first LSD of the Royal Navy came from a design by Sir Roland Baker who had designed the British Landing Craft, Tank. It was an answer to the problem of launching small craft rapidly. The "Landing Ship Stern Chute", which was a converted train ferry, was an early attempt. Thirteen Landing Craft Mechanized (LCM) could be launched from these ships down the chute. The Landing Ship Gantry was a converted tanker with a crane to transfer its cargo of landing craft from deck to sea - 15 LCM in a little over half an hour.
The design was developed and built in the US for the USN and the Royal Navy. The LSD could carry 36 LCM at 16 knots. It took one and a half hours for the dock to be flooded down and two and half to pump it out. When flooded they could also be used as docks for repairs to small craft.
Vessels of the LSD hull classification
In the United States Navy, two related groups of vessels classified as LSDs are in service as of 2011, the Whidbey Island and Harpers Ferry classes, mainly used to carry hovercraft (LCACs), operate helicopters, and carry Marines.
The British Royal Fleet Auxiliary (RFA) operates three Bay-class landing ships based on the Dutch-Spanish Enforcer design in support of the Royal Navy's operations, while a fourth ship of the class - previously in RFA service - is now operated by the Royal Australian Navy.
Former US LSDs include the Ashland class, Casa Grande class, Thomaston class and Anchorage class.