Starting in the late 1960s, planning began for a new class of patrol boat to replace the "Attack" class, with designs calling for improved seakeeping capability, and updated weapons and equipment. The "Fremantle"s had a full load displacement of , were long overall, had a beam of , and a maximum draught of . Main propulsion machinery consisted of two MTU series 538TB91 V16 diesel engines, which supplied to the two propeller shafts. Exhaust was not expelled through a funnel, like most ships, but through vents below the waterline.