The
Acastas were larger and heavier armed than the preceding H and I classes ( and , respectively), displacing about 25% more and with the mixed calibre armament replaced with a uniform fit of
QF 4-inch guns, which the
Acastas introduced. Previous weapons had been of the breech-loading (
BL) type. The 4-in guns were shipped one on the
forecastle and one at the stern, as in the
Acheron class, while the third was variously sited on the centreline between the two torpedo tubes or abaft both. All ships had three funnels, the foremost being tall and narrow, the second short and wide and the third level with the second but narrower. The foremost torpedo tube was sited between the second and third funnels, a distinctive feature of this class. There were twelve 'standard' vessels built to a common Admiralty design, and eight builders' specials that (except for
Garland) had a shorter, less beamy hull; five of the latter were from
Thornycroft with (one of Thornycroft's ships, , was planned to
diesel cruising motors, but these were not ready in time and
Hardy was completed with Thornycroft's standard machinery). One by
Parsons () had semi-geared turbines giving a speed of on trials, with a seventh from
Fairfields had a clipper
bow. The eighth 'special' was by
William Denny, Dumbarton, which was built using
longitudinal framing rather than conventional transverse framing. While
Ardent novel construction seems to have been a success, no more destroyers were built for the Royal Navy using longitudinal framing until the
J-class destroyers in the 1930s. ==Service==