Destroyer escort (DE) was the United States Navy mid-20th-century classification for a 20-knot (37 km/h; 23 mph) warship designed with the endurance necessary to escort mid-ocean convoys of merchant marine ships. 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 1975. From circa 1954 until 1975 new-build US Navy ships designated as destroyer escorts (DE) were called ocean escorts. Destroyer escorts and frigates were mass-produced for World War II as a less expensive antisubmarine warfare alternative to fleet destroyers. Similar types of warships in other navies of the time included the 46 diesel-engined Kaibōkan of the Imperial Japanese Navy., 10 Kriegsmarine escort ships of the F-class and the two Amiral Murgescu-class vessels of the Romanian Navy.
Postwar destroyer escorts and frigates were larger than those produced during wartime, with increased antiaircraft capability, but remained smaller and slower than postwar destroyers. As Cold War destroyer escorts became as large as wartime destroyers, the United States Navy converted some of their World War II destroyers to escort destroyers (DDE).
Full-sized destroyers must be able to steam as fast or faster than the fast capital ships such as fleet carriers and cruisers. This typically requires a speed of 25–35 knots (46–65 km/h) (dependent upon the era and navy). They must carry torpedoes and a smaller caliber of cannon to use against enemy ships, as well as antisubmarine detection equipment and weapons.
A destroyer escort needed only to be able to maneuver relative to a slow convoy (which in World War II would travel at 10 to 12 knots (19 to 22 km/h)), and be able to defend against aircraft, and detect, pursue, and attack submarines. 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. Their much slower speed was not a liability in this context, since sonar was useless at speeds over 20 knots (37 km/h).
As an alternative to steam-turbine propulsion found in 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 (which 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.
The Tacoma-class patrol frigates (PF) had a greater range than the superficially similar destroyer escorts, but the US Navy viewed them as decidedly inferior in all other respects. The Tacoma class had a much larger turning circle than a destroyer escort, lacked sufficient ventilation for warm-weather operations – a reflection of their original British design and its emphasis on operations in the North Atlantic Ocean – and were criticized as far too hot below decks, and, because of the mercantile style of their hulls, had far less resistance to underwater explosions than ships built to naval standards like the destroyer escorts.
Destroyer escorts were also useful for coastal antisubmarine and radar picket ship duty. During World War II, seven destroyer escorts (DEs) were converted to radar picket destroyer escorts (DERs), supplementing radar picket destroyers. Although these were relegated to secondary roles after the war, in the mid-1950s, 12 more DEs were converted to DERs, serving as such until 1960–1965. Their mission was to extend the Distant Early Warning Line on both coasts, in conjunction with 16 Guardian-class radar picket ships, which were converted Liberty ships.
During World War II, some 95 destroyer escorts were converted by the US to high-speed transports (APDs). This involved adding an extra deck which allowed space for about 10 officers and 150 men. Two large davits were also installed, one on either side of the ship, from which landing craft (LCVPs) could be launched.
The Lend-Lease Act was passed into law in the United States in March 1941, enabling the United Kingdom to procure merchant ships, warships, munitions, and other materiel from the US, to help with the war effort. This enabled the UK to commission the US to design, build, and supply an escort vessel that was suitable for antisubmarine warfare in deep open-ocean situations, which they did in June 1941. Captain E.L. Cochrane of the American Bureau of Shipping came up with a design which was known as the British destroyer escort (BDE). The BDE designation was retained by the first six destroyer escorts transferred to the United Kingdom (BDE 1, 2, 3, 4, 12, and 46); of the initial order of 50, these were the only ones the Royal Navy received, the rest being reclassified as destroyer escorts on 25 January 1943 and taken over by the United States Navy.
When the United States entered the war, and found they also required an antisubmarine warfare ship and that the destroyer escort fitted their needs perfectly, a system of rationing was put in place whereby out of every five destroyer escorts completed, four would be allocated to the U.S. Navy and one to the Royal Navy.
After World War II, new-build United States Navy destroyer escorts were referred to as ocean escorts, but retained the hull classification symbol DE. However, other navies, most notably those of NATO countries and the USSR, followed different naming conventions for this type of ship, which resulted in some confusion. To remedy this problem, the 1975 ship reclassification declared ocean escorts (and by extension, destroyer escorts) as frigates (FF). This brought the USN's nomenclature more in line with NATO, and made comparing ship types with the Soviet Union easier. As of 2006, no plans existed for future frigates for the US Navy. USS Zumwalt and the littoral combat ship (LCS) were the main ship types planned in this area. However, by 2017 the Navy had reversed course, and put out a Request For Proposals (RFP) for a new frigate class, temporarily designated FFG(X). One major problem with ship classification is whether to base it on a ship's role (such as escort or air defense), or on its size (such as displacement). One example of this ambiguity is the Ticonderoga-class air-defense ship class, which is classified as cruiser, though it uses the same hull as the Spruance-class destroyers.
During the Vietnam War, the Republic of Vietnam Navy received two Edsall-class destroyer escorts from the United States.
Six Cannon-class destroyer escorts were built for the Free French Navy. Although initially transferred under the Lend-Lease Act, these ships were permanently transferred under the Mutual Defense Assistance Program (MDAP).
Under the MDAP the destroyer escorts leased to the Free French were permanently transferred to the French Navy. In addition, the following navies also acquired DEs:
The table below compares destroyer escorts and frigates designed for similar missions.
|River-class frigate||1942||UK||1,370 tons||20 knots||151|||
|Type A kaibōkan||1943||Japan||870 tons||19 knots||18|||
|FMR class||1943||US||1,200 tons||21 knots||85|||
|Evarts-class||1943||US||1,140 tons||21 knots||72|||
|Buckley-class||1943||US||1,400 tons||23 knots||102|||
|Cannon-class||1943||US||1,240 tons||21 knots||72|||
|Tacoma-class frigate||1943||US||1,430 tons||20 knots||96|||
|Type B kaibōkan||1943||Japan||940 tons||19 knots||37|||
|Loch-class frigate||1944||UK||1,435 tons||20 knots||30||anti-submarine|
|WGT class||1944||US||1,350 tons||24 knots||87|||
|TEV class||1944||US||1,450 tons||24 knots||22|||
|Bay-class frigate||1945||UK||1,580 tons||20 knots||26||anti-aircraft, built on Loch class hulls|
|Dealey class||1954||US||1,450 tons||25 knots||13|||
|Type E50 frigate||1955||France||1,290 tons||28 knots||4||fast|
|Type 14 'Blackwood' frigate||1955||UK||1,180 tons||24 knots||15||"second-rate" anti-submarine warfare frigates. Cheaper to produce than Type 12.|
|St. Laurent class||1955||Canada||2,263 tons||28 knots||7||anti-submarine|
|Type B||1956||Japan||1,070 tons||25 knots||2||diesel|
|Type 12 'Whitby' frigate||1956||UK||2,150 tons||31 knots||6||anti-submarine|
|Type E52 frigate||1956||France||1,295 tons||28 knots||14||fast|
|Almirante Clemente-class light destroyer||1956||Venezuela||1,300 tons||32 knots||6||fast|
|Type 61 'Salisbury' frigate||1957||UK||2,170 tons||24 knots||4||aircraft direction|
|Canopo-class frigate||1957||Italy||1,807 tons||26 knots||4|||
|Type 41 'Leopard' frigate||1957||UK||2,300 tons||24 knots||7||anti-aircraft escort for convoys|
|Azopardo-class frigate||1957||Argentina||1,160 tons||20 knots||2|||
|Restigouche class||1958||Canada||2,366 tons||28 knots||7||anti-submarine|
|Claud Jones class||1959||US||1,450 tons||22 knots||4|||
|Type 12M 'Rothesay' frigate||1960||UK||2,380 tons||30 knots||12||."Modified" Type 12. Anti-submarine|
|Köln-class frigate||1961||Germany||2,100 tons||30 knots||6||fast|
|River-class destroyer escort||1961||Australia||2,100 tons||30 knots||6||Originally designated as anti-submarine frigates, later re-designated as destroyer escorts.|
|Isuzu-class destroyer escort||1961||Japan||1,490 tons||25 knots||4|||
|Type 81 'Tribal' frigate||1961||UK||2,300 tons||28 knots||7||general purpose|
|Bergamini-class frigate||1961||Italy||1,410 tons||26 knots||4|||
|Commandant Rivière-class frigate||1962||France||1,750 tons||25 knots||13||dual purpose|
|Mackenzie class||1962||Canada||2,366 tons||28 knots||4||anti-submarine|
|Hvidbjørnen-class frigate||1962||Denmark||1,345 tons||18 knots||4||fishery protection|
|Type 12I 'Leander' frigate||1963||UK||2,450 tons||30 knots||26||"Improved" Type 12. General purpose.|
|Bronstein class||1963||US||2,360 tons||26 knots||2|||
|Garcia class||1964||US||2,620 tons||27 knots||10|||
|Oslo-class frigate||1966||Norway||1,450 tons||25 knots||5|||
|Brooke class||1966||US||2,640 tons||27 knots||6||guided missile|
|Peder Skram-class frigate||1966||Denmark||2,030 tons||28 knots||2||fast|
|Van Speijk-class frigate||1967||Netherlands||2,200 tons||28 knots||6|||
|Alpino-class frigate||1968||Italy||2,000 tons||28 knots||2|||
|Alvand-class frigate||1968||Iran||1,110 tons||40 knots||4|||
|Knox class||1969||US||3,011 tons||27 knots||46|||
|Chikugo-class destroyer escort||1971||Japan||1,470 tons||25 knots||11|||
Five destroyer escorts are preserved as museum ships, while others remain in active service.