HMS Swift was the first destroyer leader of the RN that was a destroyer herself; the RN previously (and, due to Swift's disappointing performance, afterwards as well, till a really satisfying leader design became available in shape of the Marksman-class (see above)) preferred light cruisers as flotilla leaders. Designed for a kind of performance that was beyond the technical possibilities of her day, Swift took more than three years to complete and run trials; numerous modifications had to be made, and yet she failed to attain her design speed and always remained a fuel hog. With four 102mm guns and two single 457mm torpedo tubes, she was exceptionally poorly armed for her size. Despite her roomy hull, she was not very comfortable, because her engines ate up enormous volume. On the plus side, her high freeboard made her a very good sea boat.
During the war, an attempt was made to make better use of her size by arming her with a single 152mm gun forward; the two 102mm pieces mounted abreast in front of the bridge were landed. Her bridge was strengthened and enlargened, a second searchlight amidships was added and the remaining 102mm guns received partial gunshields. A line drawing of her 1916 state also shows something that looks like a 47mm (3pdr) gun on a HA mount aft, but I found no mention of AA guns in any published source I have access to. The 152mm gun was no success, and the original armament was again mounted in 1917. Structurally weak as she was, HMS Swift was quickly discarded after the war.