This volume is devoted to the sloops of the Black Swan class and its improved derivatives, widely regarded as the 'Rolls-Royce' of World War II convoy escorts. Heavily armed and superbly equipped for their role, they were among the most effective anti-submarine ships of the battle in the Atlantic. The design was gradually improved and this book uses plans of four selected ships to chart that development. These comprise: Black Swan as built; Flamingo as modified later; Starling, the single most successful U-boat hunter of the war, as in 1943; and Amethyst, as refitted after her clash with Chinese communists on the Yangtze in 1949.