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 3adj=onNaNadj=on guns were used as the main surface armament in the Tacoma- and Colony-class frigates instead of the British QF 4adj=onNaNadj=on 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.[1] Upon transfer to the Royal Navy, each ship underwent modifications to bring her in line with Royal Navy requirements.
Uniquely among the Colony-class frigates, and indeed among all World War II frigates, HMS Caicos was fitted and used as an aircraft detection frigate, stationed in the North Sea to detect V-1 flying bombs targeted against Great Britain. The other 20 ships served on patrol and convoy escort duties during the latter part of World War II. The ships are mentioned in HM Frigate by Nicholas Monsarrat, a very slim volume published under wartime censorship rules.
Post-war, the Royal Navy returned one of the ships to the U.S. Navy in 1945 and the rest during 1946. None saw U.S. Navy service. Two of the ships were sold into mercantile service in Egypt, surviving until 1956, and Caicos was sold to Argentina in 1947 and served in the Argentine Navy until 1969. The United States scrapped the rest between 1947 and 1949, as they were considered inferior to destroyer escorts, which the U.S. Navy had in ample numbers, in every aspect except range.
With date returned to the United States (unless otherwise stated). Almost all were scrapped by 1946 or 1947, unless stated.