 The "Rothesay" class was an improved version of the anti-submarine frigate, with nine "Rothesay"s ordered in the 1954–1955 shipbuilding programme for the Royal Navy to supplement the six "Whitby"s.

"Rhyl" was long overall and between perpendiculars, with a beam of and a draught of .The "Rothesay"s were powered by the same Y-100 machinery used by the "Whitby" class.Two Babcock & Wilcox water-tube boilers fed steam at and to two sets of geared steam turbines which drove two propeller shafts, fitted with large ( diameter) slow-turning propellers.