Within the past few years the dock landing ship with her unusual hull form has become the most versatile as well as perhaps the most important unit in our amphibious forces. A somewhat similar unusual hull form was originally conceived for an entirely different purpose. The French Navy built the Kangourou in the early twentieth century with a bow capable of opening and providing access to a drydock inside the hull. It was designed to transport and drydock two small submarines. By flooding its tanks to the right degree the bow was immersed so as to permit the entrance and exit of self-propelled submarines. The Kangourou can be considered the mother of modern ships for the rapid on and off loading of tanks, cargo, and vehicles.
As soon as it became apparent that they had succeeded in the Battle for Britain, the English diverted a part of their effort towards devising ways and means of regaining bases on the continent. Designs for slow small craft tank carriers were developed—among them the MK III TLC with a length of 190 feet, a beam of 34 feet, and a displacement of 300 tons when carrying tanks. Needing a larger ship that would be able to transport these slow tank carriers to their destination at high speed and under all weather conditions, the English determined to investigate the dock type ship. Through lend-lease, arrangements were made for the Bureau of Ships to develop a design for such a ship to carry three MK III TLCs. The preliminary design, developed by the Bureau of Ships in November of 1941, emphasized short cut production procedures. Any reasonable feature that would shorten construction time was adopted even at the expense of desirable ship characteristics. For example, as many straight plates as possible were used to reduce the time required for shaping plates to normal ship lines with the result that the hull form became more resistful and exacted a speed loss. On the whole, however, the design was most satisfactory for the ship’s specified mission. On December 12, 1941, eight such ships were authorized for the U. S. Navy. Three days later the British ordered seven ships for as early delivery as possible. The major characteristics of these ships were as follows:
Length |
454 feet |
Maximum beam |
72 feet |
Draft |
14 feet |
Full load displacement |
7,100 tons |
Shaft horsepower |
7,000 |
Sustained speed |
15 knots |
The special feature of this type ship was its ability to flood down so that the well-deck was covered with water up to about nine feet. In this condition, small craft and ships as large as the landing ship medium (LSM) could enter the well under their own power. Although ideal for this purpose, the ship was not an economical cargo carrier. Many ballast tanks were required for the docking operation with the result that despite its size the ship’s cargo was limited to about 1,500 tons.
Relatively few shipyards were available to build ships of this size. Due to the demands placed on the shipyards by the need for large combatant type ships, possible locations for building the LSD were still further limited. Assignments of the first fifteen ships were made to two shipyards: Newport News Shipbuilding and Dry Dock Company and Moore Dry Dock Company. Although LSDs were the first landing ships approved for construction, they were not delivered in time to permit sufficient training and operational evaluation and still participate in the Normandy invasion. Their wartime operations were limited to Pacific areas.
All told 25 of these ships were constructed. The first eight (LSD 1-8) had Skinner uniflow reciprocating steam machinery; the remainder had steam turbines. Only the LSDs 9-12, inclusive, were delivered to the British. Most of the rest participated in numerous landings in the Pacific. Shortly after the first ship was completed, the value of this type as a repair ship for landing craft was recognized and utilized to the maximum extent compatible with the design.
In late 1950 as an outgrowth of Korean operations a new design LSD was initiated. The result was the LSD-28 (Thomaston-class) of which eight ships have so far been constructed. All features of the first LSDs that stood the test of long service evaluation were incorporated in the new ships. A new requirement for about five knots more speed exerted the greatest influence in their design. With adequate shipbuilding facilities and more skilled workmen available, the somewhat angular and irregular lines that characterized LSDs 1-27 gave way to more normal ship lines and an associated less resistful hull form. Despite this improvement, the power of the main propulsion plant had to be increased by a factor of about three to give the ship the additional speed desired. The Thomaston-class has a geared turbine propulsion plant but, unlike her predecessors, all the machinery is located beneath the well deck inboard of the ballast tanks, in better protected and more nearly normally dimensioned machinery spaces.
The ship’s landing craft capacity was increased somewhat, and in speed and ease of handling these craft have been considerably improved. In the ballasted condition the depth of water in the well is greater so that docking operations are rendered easier. The ballasting and de-watering systems have been improved so that the time of each operation is at least cut in half. The stern gate design incorporated all improvements which service experience with the earlier ships showed to be advantageous.
Not only have the hull lines and with them the ship’s buoyancy capabilities been changed so as to greatly increase its cargo deadweight capacity but also arrangements have been made to provide stowage space for added cargo. The Thomaston is fitted with a removable mezzanine deck that can support about 200 tons of wheeled vehicles. In addition, a removable superdeck is installed that can carry about 400 tons of vehicles or other cargo. A portable ramp can be rigged from the superdeck to the mezzanine deck or from the mezzanine deck to the well deck for loading or unloading operations. Some of these features were previewed to a certain extent in older LSDs via the alteration route.
The Thomaston bow structure has been strengthened for cold weather operation. She has two 50-ton precision handling cranes that are useful for handling miscellaneous cargo, vehicles, LCM (6)s and helicopters. A helicopter facility is incorporated in the design. While the Thomaston itself is not air conditioned, the seventh and eighth ships of this class are provided with this important habitability feature. The ship is much better equipped to perform minor repairs on landing craft as well as underwater repairs.
The LSD type is now perhaps the most important unit of our amphibious fleet. Its use has suggested other possible important applications. The LPD, a new ship using this same hull form, is included in the 1959 Shipbuilding Program. Two LPDs will have approximately the same carrying capacity as an APA and an AKA but at the same time will have considerably greater flexibility. Although their well decks will be smaller, they will still have the same general facility for handling large landing craft as their parent, the LSD. In addition, the LPD will have helicopter facilities, considerable vehicle capacity and carry a sizable number of marines. Tests conducted with the P5M have shown that the LSD type can be converted to tend seaplanes more efficiently than the older style seaplane tenders; one such conversion (AVD) is included in the 1959 Shipbuilding Program. Other uses suggest themselves and in this respect the Bureau of Ships is now investigating a possible new basic LSD hull—one hull form that would be adaptable for several basic types; namely: LSD, LPD, AV, AGC and AKD.
Over the years the versatility of the LSD has steadily increased. Everything points to further uses for this type in one form or another for the navy of the future.