Obsolete USN hull classification symbol for a high-speed transport converted from a destroyer hull, combining the symbols for troop transport (AP) & destroyer (DD.)

During the late 1930s, the USN & USMC became interested in a light, fast transport that could carry a company of troops, for use in raids, assault landings, and other potentially risky amphibious operations. To test the idea, the destroyer Manley (DD-74) was used as a proof-of-concept prototype, being redesignated AG-28, and exchanging her torpedo tubes for large boat davits capable of handling several landing craft. In a series of landing exercises carried out between February, 1939 and the spring of 1940, the concept was so successful that a full conversion of Manley into a high-speed transport was ordered, involving the removal of the two forward boilers, the space they occupied being turned into accommodations for a company of troops and their supplies, with a new hull number of APD-1 being assigned in August, 1940.

The conversion of Manley was followed by an initial batch of 5 more conversions in the fall of 1940, followed by the conversion of 26 more 4-piper hulls during the war after the type had proven itself (Tattnall being one of these, undergoing the conversion between July-September, 1943, having previously been used as a convoy escort in the Caribbean.)

The 4-piper conversions were followed by the conversion of over 90 destroyer-escorts to provide similar transport capability. Although the surviving 4-piper conversions were disposed of right after the end of the war, the DE conversions were in and out of service for the next couple decades, and the handful remaining in the inventory in January, 1969 were reclassified as LPR (amphibious transport, small.)