The ships were built as United States Navy patrol frigates, a design that was an adaptation of the Royal Navy design built in UK, Canada and Australia, with modifications made mainly to use materials and parts more readily available in the United States. For example, American guns were used as the main surface armament in the Tacoma- and Colony-class frigates instead of the British QF Mk XIX guns of the River-class. They were mass-produced to mercantile standards to enable their speedy construction in shipyards that did not normally build warships. They were built more quickly than British shipyards could build the Rivers, but the quicker build required more man-hours and sterling cost was about twice that of a River.Brown, DK Nelson to Vanguard Upon transfer to the Royal Navy, each ship underwent modifications to bring her in line with Royal Navy requirements.
