[1] The U-class were War Emergency Programme destroyers, intended for general duties, including use as anti-submarine escort, and were to be suitable for mass-production.

At the same time, the relatively recent War Emergency destroyers, with their low-angle guns and basic fire control systems, were considered unsuitable for modern warfare, so it was decided to convert these obsolete destroyers into fast escorts, acting as a stop-gap solution until new-build ships, such as the Type 12 frigates could be built in sufficient numbers.

[9][10] The revised ships had a much reduced gun armament of one twin 4-inch (102 mm) anti aircraft mount aft of the main superstructure and one twin Bofors mount, but anti-submarine equipment was as fitted to the Type 12s, with Undaunted being fitted with two Limbo anti-submarine mortars, directed by Type 170 and 172 sonar.

Built as a destroyer of 1,710 tons, most of her first ship's company joined her in February 1944, after travelling by overnight troop train from Devonport Barracks.

She operated in the North Cape area where she escorted the aircraft carriers Furious, Victorious, Emperor, Fencer, Searcher and Pursuer with other escorts, including the battleship Anson, cruisers Belfast, Jamaica, Sheffield, Royalist, destroyers Meteor, Milne, Onslaught, Ursa, Verulam, Vigilant, Virago and Wakeful.

It was while she was at Normandy that the recently appointed Supreme Allied Commander in Europe, General Dwight D. Eisenhower was embarked in her from the fast mine laying cruiser Apollo, which had grounded, damaging her propellers.

General Eisenhower and Admiral Ramsay were given a fast passage back to Portsmouth by Undaunted and his flag was a Wardroom "Trophy" until 1969, when it was presented to the National Trust for Scotland during a ceremony in Edinburgh, during a visit to Leith.

During the afternoon of 7 June 1944, HMS Undaunted embarked General Eisenhower, Admiral Ramsay and their staffs, whose ship had grounded.

General Eisenhower signed his name across two of the stars, using an indelible pencil dipped in whiskey.After D-Day, Undaunted saw service in the Mediterranean and did a great deal of escort work out of Malta.

As part of the British Pacific Fleet she was assigned the pennant number D25, she acted as Guard ship off Yokohama Bay on VJ Day, whilst the peace treaty was being signed aboard the US battleship USS Missouri.

Shortly after VJ Day, Undaunted sailed into Sydney, Australia, flying the flags of Japan, Germany and Italy.

In January 1946, she sailed home via Sydney, Melbourne, Cape Town, St Helena, Freetown and Gibraltar, to Plymouth, where she arrived on 19 March 1946.

[14][15] She was fitted with a flight deck in 1959 and became the first small ship in the Navy trials to carry an anti-submarine helicopter - the naval version of the Saro P.531, later developed into the Westland Wasp.