Development of the destroyer escort was promoted by the British need in World War II for anti-submarine ships that could operate in open oceans at speeds of up to 20 knots. These "British Destroyer Escort"s were designed by the US for mass-production under Lend Lease as a less expensive alternative to fleet destroyers. The Royal Navy and Commonwealth forces identified such warships as frigates , and that classification was widely accepted when the United States redesignated destroyer escorts as frigates FF in From circa until new-build US Navy ships designated as destroyer escorts DE were called ocean escorts.
Postwar destroyer escorts and frigates were larger than those produced during wartime, with increased anti-aircraft capability, but remained smaller and slower than postwar destroyers. Full-sized destroyers must be able to steam as fast or faster than fast capital ships such as fleet carriers and cruisers. They must carry torpedoes and a smaller caliber of cannon to use against enemy ships, as well as antisubmarine detection equipment and weapons.
These lower requirements greatly reduce the size, cost, and crew required for the destroyer escort. Destroyer escorts were optimized for antisubmarine warfare, having a tighter turning radius and more specialized armament such as the forward-firing Hedgehog mortar than fleet destroyers. As an alternative to geared steam-turbine propulsion found in sloops of similar purpose, size and speed as well as full-sized destroyers and larger warships , many US destroyer escorts of the World War II period had diesel-electric or turboelectric drive , in which the engine rooms functioned as power stations supplying current to electric motors sited close to the propellers.
Electric drive was selected because it does not need gearboxes produced on special precise machining tooling available in limited quantities, they were heavily in demand for the fast fleet destroyers to adjust engine speed to the much lower optimal speed for the propellers.
The current from the engine room can be used equally well for other purposes, and after the war, many destroyer escorts were re-used as floating power stations for coastal cities in Latin America under programs funded by the World Bank.
