Before the United States entered World War II, as newer and more modern destroyers joined the fleet, some older destroyers were refitted for other duties: as seaplane tenders, destroyer minelayers, or destroyer minesweepers, and in an innovation, as fast transports carrying fully equipped troops for assault landings. During the war, newly built or unfinished destroyer escorts were converted to APDs.
"Flush-deck" conversions
The first group of APDs were converted from one, 17, and 14 "flush-deck" destroyers built during and after World War I. Some of these had been previously converted to aircraft tenders or other uses. In the conversion, the two forward boilers were removed along with their smokestacks. Accommodation for 200 troops was installed in the former engine spaces. The original armament of four 4-inch guns, one 3-inch AA gun, and twelve 21-inch torpedo tubes was replaced with three modern 3-inch AA guns, one 40 mmAA gun, and five 20 mmAA guns. Two depth charge racks and up to six K-gun depth charge throwers were carried. In place of the torpedo mounts, four davit-mounted LCPLs were shipped. Later, the LCPLs were replaced by a version with a bow ramp, the LCPR.
''Buckley''-class conversions
The second group of APDs were converted from 43 s s built in 1943-1945. Two further planned conversions were canceled at the end of the war. These converted vessels were known as the Charles Lawrence class. In the conversion, the superstructure was expanded to provide accommodation for 162 troops. The original gun armament of three 3-inch AA guns and six 20 mm AA guns was replaced with one 5-inch DP gun and six 40 mm AA guns. The Charles Lawrence class retained the original three torpedo tubes, and carried two depth charge racks and up to eight K-guns. Typically, the converted DEs carried four LCVPs in a stacked davit configuration.
''Rudderow''-class conversions
The third group of APDs were converted from 51 s built in 1943-1945. All but one of these were converted while under construction. These converted vessels were known as the. This conversion was the same as the Buckley class, except that the original armament had two 5-inch DP guns instead of three 3-inch guns; the aft 5-inch gun was removed.
In the Guadalcanal Campaign, neither side enjoyed the overwhelming local naval and air supremacy which ensured victory in every other amphibious operation of the war. This necessitated an increase in the number of high-speed transports, hybrid warships which combined the functions of transports and destroyers. The concept of the high-speed transport embodied sufficient armament for the ship to defend herself against smaller warships and to support the troops she carried with sufficient speed to enable her to outrun more heavily armed ships. APDs performed arduous service. They transported troops to beachheads, served as escorts for transports and supply vessels, conducted anti-submarine patrols and survey duties, operated with Underwater Demolition Teams and commando units, performed messenger and transport duties, conveyed passengers and mail to and from forward units, and were involved in minesweeping operations. They were attacked by submarines, surface ships and aircraft, and many were damaged or sunk.
After World War II
Nine "flush deck" APDs were lost during the war. The remaining 23 were scrapped in 1945-1946. Some of the Charles Lawrence-class and Crosley-class APDs saw service in the Korean War and Vietnam War. One Charles Lawrence-class APD was lost during World War II. 14 were transferred to foreign navies in the 1960s. One was sold for commercial use as a floating power station. 26 were scrapped. On 1 January 1969, the remaining three were reclassified as "Fast Amphibious Transports". No Crosley-class APD was lost during World War II. 18 were transferred to foreign navies. One was lost in a collision in 1966. Eight were sold as floating power stations. 18 were scrapped. In 1969, the remaining eight were reclassified as "Fast Amphibious Transports".
