This class was the climax of the design pattern initiated with the "Bittern" class, and the principle change was the replacing of the quarterdeck 4" gun with a quad pom-pom to improve close in air defence.
The early pair of ships, the Black Swan and Flamingo were launched with tripod masts fore and aft and a quad machine-gun on either side amidships. These were soon replced by single 20mm Oerlikons, and a Hedgehog mortar was placed on the shelter deck, and the mainmast was replaced with a lattice mast forward with SW type 271 RDF and AW type 286. AR type 285 was fitted to a HA.DCT.
The second pair were completed like the Black Swan and Flamingo were modified.
Soon, in all but the war loss Ibis, additional single 20mm cannons were added in the wings, and to replace the amidships single with powered twins, and the foremast was replaced by a lattice mast carrying SW 291 RDF.
These four originals were followed by the "Modified" type, although the additional equipment carried and stresses on the hulls of this type made them not as succesful or popular than their forebearers. Nevertheless, in escort groups containing an escort carrier and some frigates, they roved the Atlantic to bolster convoys needing support, and had, by 1944, the U-boats on the run, in conjunction with RAF long range planes and the overshadowed and unglamarous convoy escorts.
The main difference was the omitting of the pom-pom for a uniform AA armament of 20mm cannnons; two single in the wings and two twins in both the amidships and quarterdeck tubs. However, wartime shortages led to the adoption of anything that was available; see tables below. Postwar completions had 40mm Bofors in the wings, and no quarterdeck guns.
A lattice foremast carried AW type 291 and SW type 271 RDF, replacing a planned fore and aft tripod layout.
The main additional load was 110 DC's aft, and hard driven in the North Atlantic, deck and hull cracking became apparent, and the welds became loose. No solution could be found, there was no time to lay them up and fix the hulls, and they carried on. Fortunately, they were far too expensive and complex for mass production, and the bulk of escorts were made up of the simple, reliable and effective corvettes, frigates and escort destroyers.
They are remembered as the "capital ships" of the escort fleet, and for some reason, hlaf way through the clas, the newly adopted bird name pattern was dropped for traditional small ship names.