Full size destroyers must be able to keep up with and exceed the speed of fast capital ships, typically needing better than 35 knot speeds and carrying torpedoes to use against enemy ships, as well as anti-submarine detection equipment and weapons.
A destroyer escort need only be able to maneuver relative to a slow convoy, which in World War II would travel at 10 to 12 knots, to defend itself against aircraft, and to detect, chase down and attack a submerged or surfaced submarine. These lower requirements greatly reduce the size, cost and crew required for the destroyer escort.
Like their larger sister ships, destroyer escorts have almost no armor.
Destroyer escorts are also useful for coastal anti-submarine and radar picket ship duty.
For an excellent book on the subject of a particular example of this type of ship (USS Abercrombie (DE-343)) in World War II see Little Ship, Big War: The Saga of DE-343 by Edward Peary Stafford. Naval Institute Press, 2000 ISBN 1557508909
The capability of submarines to interdict their enemy's supply lines and to destroy his ability to wage war was the single reason for the inception of the destroyerescort.
Since the destroyer was the only surface fleet unit that could effectively locate, attack and destroy a submarine, it was logical that we should develop a destroyer type that would concentrate on the submarine and thereby release destroyers for fleet assignment.
Astern waited another escort ready to move into the fueling position as soon as it was clear and also to act as a rescue ship in case of a man overboard during the hazardous evolution.
A DestroyerEscort (DE) is classification for a small, comparatively slower warship designed to be used to escortconvoys of merchant marine ships, primarily of the United States Navy in World War II.
The Royal Navy also used destroyerescorts but classified them as the Captains class frigate, although somewhat confusingly they referred to the Hunt class and similar ships as "escortdestroyers".
The destroyerescorts played a major role in breaking the back of the German and Japanese submarine fleets and, together with APDs, contributed heavily to the defense against the kamikaze corps.