'Dukedom' was a British naval undertaking by Vice Admiral Sir Arthur Power’s East Indies Fleet to locate and destroy the Japanese heavy cruiser Ashigara, destroyer Kamikaze and several submarine chasers (10/14 May 1945).

On 10 May Vice Admiral H. T. C. Walker’s Force 61 1 departed Trincomalee on the east coast of Ceylon in search of the two Japanese warships, which had left Singapore earlier on the same day and been reported by the British submarines Statesman and Subtle as they shaped course to the north-west through the Malacca Strait with the probable objective of evacuating the Japanese garrisons of the Andaman and Nicobar island groups. The warships of Force 61 were supported by Force 70, which comprised the oiler Easedale escorted by the destroyer Paladin.

Walker intended to intercept the two Japanese warships in the Eleven Degrees Channel. On 11 May the escort carriers launched an attack with Grumman Hellcat fighter-bombers on the Japanese positions at Car Nicobar, but were sighted by Japanese reconnaissance aircraft whose warnings persuaded the Japanese to recall Haguro and Kamikaze, a fact signalled by Statesman, which had sighted the Japanese retiring to the south-east, probably as a result of the sighting, by Japanese aircraft on the morning of 11 May, of units of Force 61 to the west of the Nicobar islands group. In an effort to avoid being sighted again, Force 61 then proceeded to a position about 230 miles (370 km) to the south-west of Achin Head at the northern end of Sumatra, and Force 70 was ordered to rendezvous with Force 61 for refuelling.

It was appreciated that if Japanese aircraft made no further sightings of the East Indies Fleet’s ships, they might make another attempt to sortie the cruiser force.

During the afternoon of 13 May, in response to a request by Walker, all available ships were sailed from Trincomalee to reinforce Force 61. These ships were the light cruiser Nigeria and the destroyers Racehorse, Redoubt and Roebuck, which constituted Force 62. The destroyer Rocket, which was currently escorting a southbound troopship, was ordered to leave her charge and rendezvous with Force 62 on 14 May. Force 67, comprising the oiler Olwen and destroyer Penn, was also ordered to depart Trincomalee on 13 May and steam to the north-east to satisfy any need for a second oiling force.

Force 62 met Force 61 at 07.00 on 15 May.

On 14 May Walker had detached the escort carriers (Commodore G. N. Oliver’s 21^st Carrier Squadron), the heavy cruiser Cumberland and the destroyers Saumarez, Venus, Verulam, Vigilant and Virago (Captain M. L. Power’s 26^th Destroyer Flotilla) from Task Force 61 to join Task Force 62 in the area to the west of the Six Degrees Channel in continuing the search for the Japanese evacuation force and effecting the interception and destruction of the Japanese ships, now reported to be heading to the south in the Indian Ocean.

At 10.50 on 15 May, the Japanese cruiser and destroyer were sighted, retiring to the south-east, by a Grumman Avenger warplane of No. 851 Squadron, baed on Shah but currently operating from Emperor as Shah's catapult had developed a defect. Almost simultaneously, the Japanese ships were sighted by a Liberator of No. 222 Group. This was one of six such aircraft which were just beginning a parallel track search. The Liberator shadowed the Japanese ships until about 14.00. The Avenger had previously sighted and attacked a small merchant ship escorted by a submarine chaser about 17.5 miles (28 km) to the north-west of the Japanese cruiser.

At 15.00 an attack by three Avenger warplanes resulted in one probable bomb hit and one near miss being scored on the cruiser, which was then steering due east. This was the last sighting of the cruiser in daylight.

The nearest British warships at 15.00 were those of Captain M. L. Power’s 26^th Destroyer Flotilla, namely Saumarez, Venus, Verulam, Vigilant and Virago, which were 100 miles (160 km) to the west of the Japanese ships and steering a course to effect an interception after the fall of night. The British heavy ships and escort carriers were currently all to the west of Sabang.

This paved the way for 'Mitre' against what were in fact the heavy cruiser Haguro and destroyer Kamikaze.

The units of the East Indies Fleet subsequently concentrated in an area to the north of the island of Sumatra, and at the brak of day on 16 May, launched reconnaissance flights from the island of Phuket southward into the Strait of Malacca.

Several air attacks by some five Japanese fighter-bombers were made on the fleet. The attacks were not pressed home vigorously, but a near miss on Virago at sunset caused damage to the destroyer above her water line and resulted in the deaths of four men and serious injuries to another eight men. Two of the attacking aircraft were damaged by British carrierborne fighters.

The forces were reconstituted on 17 May. Half the fleet and Force 67 returned to Trincomalee, while the other half remained at sea until 19 May before starting back to Trincomalee, where they arrived on 21 May.

The light anti-aircraft cruiser Phoebe, which had been patrolling off the coast of southern Burma since 12 May with the aid of refuelling off the mouth of the China Bakir river, in 16 May established a patrol mid-way between Port Blair and Mergui to deal with any attempt by small craft to evacuate the Japanese garrison of the Andaman islands group towards the Tenasserim coast.