1:600 Scimitar modified for escort work, with 4 single Oerlikons, a 12 pound AA gun and extra depth charges aft. Note pendant ( XXI - 21 ) on funnell © Andrew Arthur

18 units of the "R" class were completed to a modified design, with twin funnels allowing the bridge to be moved farther back, leaving it much drier, and it was this feature that was the major new feature in the "S" class, an enlarged, rounded design being used. Other strange features later removed were a turtle back bulwark to the fo'c'lse and two single 18" tubes built into the bridge, firing slightly forward and across the beam. The 21" torpedo tubes, 2pdr AA gun and searchlight were also re-arranged.
During the wars, a terribly high 44 perfectly good vessels were scrapped, and 2 on the stocks broken up.
Furthermore, many were converted to menial duties, Shikari to control target battleships Agamemmnon and Centurion, and others as attendants to carriers, to targets and more. the only really valuable conversions were Stronghold, Sturdy and Thracian to 40 mine minelayers, by removing T.T's / mines and the quarterdeck 4" gun.
In 1941, they got the escort 'treatment' , the midships 4" being replaced by 2 x 4 x 0.5" MG, later 2 x 1 x 20mm Oerlikons, AS mortras and racks aft, and removing all torpedoes and the searchlight for a 12pdr AA. Later 2 further Oerlikons were added, and AW type 291 was added.

Pictures of old "R" class destroyers

Sardonyx steams out to sea, compare with above line drawing