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Landing Ship Dock / Landing Platform Dock

A Landing ship is a large type assault ship, generally over 200 feet long, designed for long sea voyages and for rapid unloading over or onto a beach. LS is the US naval prefix used to designate these ships. Prior to the 20th Century, there were no specialized landing ships or landing craft. Ridley Scott's 2010 film Robin Hood was not the worst telling of this tale, but the beach landing craft powered by oars were completely preposterous [as one reviewer noted, "why not just go the whole hog and have wooden helicopter gunships and wattle-and-daub submarines"]. Amphibious landings in the age of sail and the early decades of the age of steam were effected in ship's boats.

Many middle-tier navies are reducing their focus on surface combatants and submarines, and improving their capability in naval expeditionary warfare. There is a major increase in the number of amphibious warfare ships entering service in navies big and small, east and west. Various types of amphibious ships are being studied, on order or under construction for navies which have not operated similar warships. LPDs are emerging as key military items for Southeast Asian countries for enhancing naval defense capabilities. The LPD is designed to transport troops into a war zone by sea using landing craft. It embarks, transports and lands soldiers and landing craft and can also be used for landings by helicopters.

The US Navy faced many challenges in conducting a series of large-scale amphibious landings across the Pacific Ocean. Most Pacific islands had coral reefs that would prevent LSTs from reaching the beaches, so large numbers of small landing craft were needed to get across the reef and onto the beach. The solution was the the Landing Ship, Dock (LSD), a large cross-ocean ship that could carry both a number of troops and a large number of small landing craft (that could land all or most of the troop complement in one wave). The 475-foot ship could carry landing craft, amphibious tractors, or amphibious trucks in a well deck [the dock] that could be flooded to allow the craft to be launched under their own power through stern gates. This combination could put a lot of troops on the beach quickly (to seize a beach-head), and then the boats could come to the conventional transports and load their troops in several waves to stabilize the beach-head and expand it enough to allow a temporary pier system to be built). Subsequently, the US Navy deployed several classes of Landing Platform, Dock [LPD] which only differ in detail, not overall concept.

Landing Ship, Dock (LSD) and Amphibious Transport, Dock (LPD) have a well deck and a ballast system which allows boats to be dry docked. The LSD and LPD are generally similar in design, and while some LSDs have helicopter flight decks, the LPD have hangar space for permanently embarked helicopters [though confusingly, the first LPD-1 Raleigh had a flight deck but no aircraft hangar]. USS Shadwell (LSD-15), a Casa Grande class LSD, underwent yard period in 1952 which produced a mezzanine deck, super deck, and helicopter landing deck, and in 1959 Shadwell became the first LSD helicopter carrier, deploying to the Mediterranean in 1960 with helicopters aboard.

The term "dock" is somewhat confusing, since it might be imagined that these ships are intended to land at a dock, or transport to a dock. A dock is a water-side site at which ships tie up in order to discharge and take in cargoes conveniently and expeditiously. It is typically a basin constructed for this purpose, surrounded by quay walls. But a graving dock (or dry dock) is a dock which can be sealed off by gates, and the water removed. This allows work to be done on the parts of a ship's that are normally under water. The term "graving" was more often used to denote the cleaning of a ship's bottom. The docks in the Landing Ship, Dock (LSD) and Amphibious Transport, Dock (LPD) are internal to the ship, and allows boats to be dry docked for transport, loading and maintenance.

The stern of the LSD and LPD amphibious ships can sink up to 10 feet in order to flood its well deck with water. The stern gate is lowered and ballast tanks are filled with water, causing the controlled lowering of the aft (back) end of the ship and allowing water to enter the landing craft docking well, generally known as the well deck. Once the well deck is low enough to allow boats into the well deck, the boats are floated and secured. The water in tanks are pumped back out, resulting in the dry docking of the boat(s). The stern gate is lifted and the ship is ready to steam to its next mission. The LSD-41 class ships, for instance, can ballast down in 15 minutes and deballast in 30, with a total ballast water capacity of 12,860 tons (and full load displacement of 29,010 metric tons when in ballast). The well deck is flooded up to 6 feet forward and 10 feet aft when embarking or launching assault craft.

Dock Landing Ships (LSD) support amphibious operations including landings via Landing Craft Air Cushion (LCAC), conventional landing craft and helicopters, onto hostile shores. These ships transport and launch amphibious craft and vehicles with their crews and embarked personnel in amphibious assault operations. Amphibious Transport Docks (LPD) transport and land Marines, their equipment and supplies by embarked landing craft or amphibious vehicles augmented by helicopters in amphibious assault. These versatile ships perform the mission of amphibious transports, amphibious cargo ships and the older LSDs by incorporating both a flight deck and a well deck that can be ballasted and deballasted to support landing craft.

The first LSDs were developed during World War II and were among the most innovative amphibious ships of that war. They introduced the floodable well deck, from which a number of landing craft can be preloaded, stored, transported, launched, and recovered. Although it may not be apparent at first glance, the Landing Ship, Dock, neatly solved a variety of operational shortcomings exhibited by other types of landing ships and craft:

1. Unlike Landing craft, the LSD is an ocean-going ship and can deliver Marines and their equipment over long distances.
2. Unlike attack transports (APA) and attack cargo ships (AKA), troops and equipment can be loaded onto landing craft inside a protected well deck, rather than having boats lowered over the side with troops clambering after them. The internal dock creates a sheltered environment for the deployment of Landing Craft in adverse conditions up to Sea State 4. This feature makes operations possible at about 80 percent of the time, compared to the maximum of 30 percent attainable through alternative systems.
3. Unlike the Landing Ship Tank, the LSD does not actually go all the way to the beach, and is thus less vulnerable to coastal defense fire.
4. Unlike the Landing Ship Tank, which typically has a flat prow ramp for beaching [and a top speed of about ten knots as a result], the LSD has a sharp prow [and frequently a bow bulb], enabling tops speeds of upwards of 20 knots. This higher speed became neccessary as enemy submarines became faster over the course of World War II.
5. Unlike the Landing Ship Tank, the landing craft on the LSD can come ashore just about anywhere. The LST is restricted to favorable beaches, which in wartime reduces the element of surprise, and in peacetime limits humanitarian assistance operations.
6. Twenty-first century expeditionary warfare no longer focuses on direct beach landings and assaults. The need to land vehicles directly on a beach from a ship has been replaced by over-the-horizon assaults and ship to objective maneuver. The new strategy of over-the-horizon maneuver from the sea and ship-to-objective maneuver entails assaults which are initiated out of sight or where dangerous objectives are avoided.

Many navys around the world continue to operate LSTs, but they are generally used to perform cargo hauling missions such as those performed by the US Army's Logistics Support Vessels, which they strongly resemble in everything but name.

LPDs, along with larger LHD amphibious assault ships, feature floodable well decks able to operate small boats or landing craft. Both types can embark fully equipped combat troops and their equipment. Big-deck LHDs can operate and support helicopters, tiltrotor aircraft, unmanned aerial vehicles and vertical-takeoff-or-landing jets. LPDs in general are only able to refuel aviation assets and carry fewer troops.