Amphibious Forces
Amphibious ship class taxonomies are not precise, have changed over time, and vary from country to country. Amphibiousasault ships span a spectrum of capabilities, defined by the relative emphasis on helicopter aviation versus landing craassets for transporting troops and equipment from sea to shore. They may also be defined by the presence or absence of a bow ramp by which vehicles may be directly discharged onto the beach [a Landing Ship, Tank - LST], or by a floodeable well dock by which smaller ampbibious craft [boats, etc] may be loaded and discharged directely into the water [ a Landing Ship, Dock - LSD, or Landing Platform, Dock].
During World War II, the Allies initially lacked large, purpose-designed landing craft (essential for the distances involved),but had lots of conventional freighter & passenger ships that had been "taken up from trade". Attack transports (Navy designation APA) and attack cargo ships (AKA), originally called combat loaders, were transports (troop carriers) and cargo ships modified to carry landing craft suitable for amphibious assaults. An APA could carry a battalion of troops. Three APAs and an AKA could carry a regiment. The "Attack Transports" (APA), were later redesignated "Amphibious Transports" (LPA) and "Attack Cargo Ships" (AKA, were later redesignated "Amphibious Cargo Ships" (LKA).
During World War II a number of American destroyer escorts [DE] undwerwent conversion to a high speed transport, and were reclassified APD. The missions of such APDs were varied, and included delivert of underwater demolition teams (UDT's) to destroy obstacles on landing beaches. These high-speed transports combined the hull of a warship, a destroyer escort, with the superstructure of a troop transport designed to both carry and launch amphibious landing forces. To accomplish this dual role, a substantial length of the main deck was enclosed to house 160 troops, while a cargo hold fitted with a crane capable of handling light vehicles and equipment was added further aft. In addition, the three-tube centerline torpedo station found on the destroyer escort class was removed to make room for port and starboard boat stations capable of launching and recovering four thirty-six-foot landing boats. To make room for these structural modifications, each high-speed transport featured only one 5-inch gun for its main armament, rather than the two such weapons found on a destroyer escort.
During the Korean War, as part (Amphibious Forces Pacific, PHIBPAC) of Navy Special Operations, four of these highly specialized ships (USS Wantuck, USS Begor, USS Bass, USS Diachenko) comprised SquadronTD-111, and provided the operational catalyst for the multinational raiding force that repeatedly struck North Korea's railway system.
Landing craft are craft especially designed for beaching, unloading, or loading on a beach, and retracting. This term generally is applied to nonocean-going vessels, less than 160 feet long, designed for use in landing operations; the designation landing craft (LC) is used with appropriate modifications to designate particular types. Landing craft were ramped vessels small enough to be carried aboard APAs, AKAs, or LSTs and included several types of 36-foot vessels designed to put troops and light vehicles on the beach and 56-foot landing craft, mechanized (LCM), originally intended to carry tanks. Some rubber boats were also designated as landing craft. Amphibious vehicles included landing vehicles, tracked (LVT), which were amphibious tractors; armored LVTs mounting howitzers; and amphibious trucks, of which the most important and numerous was the DUKW, or "Duck," an amphibious 2½-ton truck.
This solution worked, but there were problems in the second phase of operations. In order to load the landing craft quickly, the troops climbed down nets and/or rope ladders (and a few stair sets) to the craft beside the transport, which led to a large number of deaths & injuries due to falls into the ocean or the landing craft.
Several countries operate military vessels that are somewhat similar to an LSD or LPD, but lack the essential defining feature of this class, the floodable well dock.
