Twenty-four ships to this design were ordered in May 1915 (numbered P.11 to P.34) and another thirty between February and June 1916 (numbered P.35 to P.64) under the Emergency War Programme[2] for the Royal Navy in the First World War, although ten of the latter group were in December 1916 altered on the stocks before launch for use as decoy Q-ships and were renumbered as PC-class sloops.

These vessels were designed to replace destroyers in coastal operations, but had twin screws, a very low freeboard, ram bows of hardened steel, a sharply cutaway funnel and a small turning circle.

With the survival of a builder's diary by William Bartram, full details of the sea trials of P.23 on 21 June 1916 exist.

A further batch of ten ships were ordered in 1917 (PC.65 to PC.70 in January, and PC.71 to PC.74 in June) as PC class sloops.

These were built to resemble small merchant vessels for use as decoy (Q) ships, and were alternatively known as "PQ" boats.