High-speed transport

High Speed Transports were converted destroyers and destroyer escorts used to support US Navy amphibious operations in World War II and afterward. They received the US Hull classification symbol APD; "AP" for transport and "D" for destroyer.

APDs were intended to deliver small units such as Marine Raiders, Underwater Demolition Teams and United States Army Rangers onto hostile shores. They could carry up to a company size unit (200 troops). They also provided gunfire support as needed.

"Flush-deck" conversions
The first group of APDs (APD-1 through APD-36) were converted from one Caldwell class, 17 Wickes class, and 14 Clemson class "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 (out of four) were removed with their smokestacks (reducing speed to 25 knots). Accommodation for 200 troops was installed in the former engine spaces. The original armament of four 4" guns, one 3" AA gun, and twelve 21" torpedo tubes was replaced with three modern 3" AA guns, one 40 mm AA gun, and five 20 mm AA 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 Landing Craft Personnel (Large) (LCPLs) were shipped. Later, the LCPLs were replaced by a version with a bow ramp, the Landing Craft Personnel (Ramped).

Buckley class conversions
The second group of APDs were converted from 45 Buckley class destroyer escorts (DE)s built in 1943-1945. 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" AA guns and six 20 mm AA guns was replaced with one 5" 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 Landing Craft Vehicle & Personnel (LCVPs) in a stacked davit configuration.

Rudderow class conversions
The third group of APDs were converted from 51 Rudderow class destroyer escorts (DE)s built in 1943-1945. All but one of these was converted while under construction. These converted vessels were known as the Crosley class.

This conversion was the same as the Buckley class, except that the original armament had two 5" DP guns instead of three 3" guns; the after 5" gun was removed.

World War II service
As newer and more modern destroyers began joining the fleet some of the old ships were assigned to other duties such as tending seaplanes, laying or sweeping mines, or for a newer innovation in modern warfare, carrying fully equipped troops for assault landings as fast transports.

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 mine sweeping operations. They were attacked by submarines, surface ships and aircraft (including kamikazes), 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" (LPR).

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" (LPR).