File:HMS Black Swan (L57) Model.jpg

English: A model of the Black Swan-Class Sloop HMS Black Swan at the Glasgow Transport Museum, 2 March 2007.

The sloop was revived as a classification in WWI with the ocean-going Flower Class originally classed as minesweepers but which were more often used as convoy escorts, and the coastal P-Boats and PC-Boats originally classed as patrol boats but which were used as A/S vessels. After WWI no more sloops were built until the old ships needed replacing in the late 1920’s. The new ocean going sloops were designed for colonial service, patrol duties and minesweeping but as successive classes were built escort duties became more and more important. Destroyers were expensive ships that weren’t particularly suitable as A/S escorts in that ASDIC (US Sonar) did not work efficiently above 20 kts so the powerful machinery and 30+ kt speed of the destroyer was wasted; neither did destroyers, with their fuel-hungry engines, have the long range necessary for escorting convoys across the North Atlantic. The sloop, however, was the ideal basis for a long range escort.

The climax of inter-war sloop development was the Black Swan Class, a minor improvement on the preceding Egret Class of three ships built in 1938. The Black Swans were multi-purpose A/S and AA escorts and minesweepers, though eventually the minesweeping gear was removed and the succeeding Modified Black Swan Class were A/S & AA escorts only. There wasn’t really a hard division between the two classes as improvements and modifications were steadily introduced almost ship-by-ship. Indeed, the last two Black Swans were hardly distinguishable from the Modified Black Swans.

Between 1939-42 13 Black Swans were launched, completed in 1939-43 and 24 Modified Black Swans were launched in 1942-46 and completed in 1943-46; 5 more of a further modified design were cancelled at the end of the war.

The original Black Swans measured 300 ft x 37.6 ft x 11 ft and had a displacement of 1,250-1,300 tons. Their 3,600 shp turbines and 2 screws gave them a speed of 19 kts. Their designed armament was 6x4” AA guns, 4x2 pdr AA pom poms (1x4) and either (first 6) 4x0.5” mg (1x4) or (second 6) 12x20 mm AA (6x2) and 40 depth charges (last two 60 depth charges) but this varied as the war progressed and depth charge stowage increased to 110.

The Modified Black Swans measured 300 ft x 38.6 ft x 11 ft and weighed 1,350 tons. Their 4,300 shp turbines gave a speed of 20 kts. As designed their armament was identical to the last 6 Black Swans except they had the capacity for 110 depth charges.

Efficient escorts though the sloops were, they were built to the Admiralty’s warship standards in yards that were familiar with the demands of warship construction whilst their turbines required specialist manufacture. The need for a mass production ocean escort was initially met by the small Flower Class corvettes (based on a commercial whaler) but there remained the need for a larger, more seaworthy, more capable escort and the result was the frigate, effectively a cross between the sloop and the corvette. It was the size of a sloop but instead of being built on high standard warship lines with precision-made turbines, was, like the Flowers, built on mercantile scantlings with unsophisticated reciprocating engines. They could be built cheaply and quickly in yards unfamiliar with warship construction. But they never displaced sloops entirely, so formidable as escorts were they.

HMS Black Swan herself was built by Yarrow Shipbuilding, Scotstoun, Glasgow, being launched in 1939 and completed in 1940. She spent the early part of the war on East Coast and participated in the Norwegian Campaign, in which she was hit by a bomb. After repair she escorted convoys in the Western Approaches, the Irish Sea, to Gibraltar and Freetown during which on a convoy to the latter port she and the Flower Class corvette HMS Stonecrop sank the top-scoring U-124. She then served on convoys to Iceland, Malta, the Mediterranean and the Adriatic. Finally, she served in the Far East and Pacific theatres. With HMS Belfast, she liberated Singapore. After the war she was severely damaged in the 1949 Yangtse Incident by shore fire. In addition, Black Swan served in the Korean War and fought in the 1950 Battle of Chumonchin Chan with the cruisers HMS Jamaica and USS Juneau in which three North Korean motor torpedo boats were sunk. She was scrapped in 1956.