The Captain class was the designation given to 78 frigates of the Royal Navy, constructed in the United States, launched in 1942–1943 and delivered to the United Kingdom under the provisions of the Lend-Lease agreement. They were drawn from two classes of the American destroyer escort (originally "British Destroyer Escort") classification: 32 of the GMT (Evarts) Type and 46 of the TE (Buckley) Type. Upon reaching the UK the ships were substantially modified by the Royal Navy, making them distinct from the US Navy destroyer escort ships.

Captain-class frigates acted in the roles of convoy escorts, anti-submarine warfare vessels, coastal forces control frigates and headquarters ships for the Normandy landings. During the course of World War II this class participated in the sinking of at least 34 German submarines and a number of other hostile craft; 15 of the 78 Captain-class frigates were either sunk or written off as a constructive total loss.

In the post-war period, all of the surviving Captain-class frigates except one (HMS Hotham which was used as a power station and for powerplant experiments) were returned to the US Navy before the end of 1947 in order to reduce the amount payable under the provisions of the Lend-Lease agreement; the last Captain-class frigate was returned to United States custody in March 1956.

It was the intention of the Admiralty that these ships would be named after captains who served with Vice-Admiral Horatio Nelson at the Battle of Trafalgar, but as building continued it became necessary to delve back further into history for the names of well-regarded admirals and captains.

Of the 78 frigates, 66 bore names that had not been allocated to earlier Royal Navy ships. Lawford, Louis, Manners, Moorsom, Mounsey, Narborough, Pasley and Seymour had been used for destroyers during World War I. HMS Rupert was the fifth of that name since 1666. Torrington was the fourth of that name since 1654. Holmes had been used once before in 1671 and Fitzroy had previously been used for a survey vessel in 1919.

In June 1941 the British government, seeking to take advantage of the US Lend-Lease program, asked the United States to design, build and supply an escort vessel that was suitable for anti-submarine warfare in deep open ocean situations. The requested particulars were a length of 300 feet (90 m), a speed of 20 knots (37 km/h), a dual purpose main armament and an open bridge. The United States Navy had been looking into the feasibility of such a vessel since 1939, and Captain E. L. Cochrane of the US Navy's Bureau of Ships – who, during his visit to the United Kingdom in 1940, had looked at Royal Navy corvettes and Hunt-class destroyers – had come up with a design for such a vessel. This design anticipated a need for large numbers of this type of vessel, and had sought to remove the major production bottleneck for such vessels: the double helical reduction gearing required for the steam turbine machinery of destroyers. The production of reduction gears could not be easily increased, as the precision machinery required for their construction alone took over a year to produce. Therefore, a readily-available and proven layout of diesel-electric machinery, also used on submarines, was adopted. When the United Kingdom made its request, Admiral Stark of the US Navy decided to put these plans into motion and recommended that the British order be approved. Gibbs and Cox, the marine architects charged with creating working plans, had to make several alterations to the production methods and to Captain Cochrane's original design, most notably dropping another production bottleneck – the 5-inch/38-caliber gun – and replacing it with the 3-inch/50-caliber gun, which allowed adding a superfiring third gun (at the "B" position, forward); also, the original design specified eight engines for 24 knots (44 km/h; 28 mph) but other priority programs forced the use of only four with a consequent shortening of the hull and reduction of the ship's maximum speed by an estimated 4 knots (7.4 km/h; 4.6 mph). The design had relatively light armour with for example the steel plate used on the Buckleys ranging from 1/2 inch to 7/16 inch with 1/4 inch plate being used for the majority of the hull and deck plating.

The result was a vessel that could be produced quickly (for example Halsted was built in just 24 and half days) at half the cost of a fleet destroyer, ($3.5 million compared to $10.4 million for a 1,620-ton destroyer such as the US Benson class or $6.4 million for British Hunt-class destroyer.)

On 15 August 1941 President Franklin D. Roosevelt authorised the construction of 50 of the new Evarts-class design as BDE 1–50 (British destroyer escort) as part of the 1799 program. The turbo-electric powered Buckley class were not part of the first order and were authorised later by Public Law 440 effective 6 February 1942. The Royal Navy placed orders in November 1941 with four shipyards: the Boston Navy Yard, the Mare Island Navy Yard, the Philadelphia Naval Shipyard and the Puget Sound Navy Yard. When the United States entered the war, they too adopted the BDE design. The BDE designation was retained by the first six destroyer escorts (BDEs 1, 2, 3, 4, 12 and 46) transferred to the United Kingdom. Of the initial 50 ordered, these were the only ones the Royal Navy received; the rest were reclassified as destroyer escorts (DE) on 25 January 1943 and taken over by the United States Navy. By the end of World War II the Royal Navy had received 31 Evarts from Boston Navy Yard, 1 from Philadelphia Navy Yard and 46 Buckleys from Bethlehem-Hingham.