'Irregular' was a British naval undertaking in the Great Passage of the Indian Ocean by Force 65 (destroyers Eskimo, Nubian, Paladin, Penn and Tartar) of Admiral Sir Arthur Power’s East Indies Fleet to intercept and destroy Japanese shipping between the Japanese-occupied Nicobar islands group and Sabang on the coast of the island of Sumatra in the Japanese-occupied Netherlands East Indies (5/10 June 1945).
The ships of Force 65 were of the 10th Destroyer Flotilla, and departed Trincomalee in Ceylon on 5 June, and on the same day, Force 64, comprising the oiler Olwen and frigate Test, departed Rangoon to act as a fuelling force in the area to the west of the Nicobar islands group.
Paladin was detached on 7 June to proceed to the Batu islands group, off the west coast of Sumatra, to carry out a special operation, and later is also proved necessary to detach Penn in order that one destroyer could be maintained constantly in the vicinity of these islands. In the course of these duties, on 12 June Penn intercepted and destroyed a Japanese landing craft containing about 20 men.
During the night of 7/8 June, Force 65 less Paladin carried out a sweep between Great Nicobar island and Sabang without result, and refuelled from Force 64 on 9 June.
On the morning of 11 June, the submarine Trident, patrolling off Diamond Point, reported a Japanese tank landing ship, escorted by a submarine chaser, headed to the north, and orders were issued for six Consolidated Liberator heavy bombers of the RAF’s No. 222 Group to undertake a search at dawn on 12 June, but shortly after the break of day on this date, Eskimo, Nubian and Tartar encountered the Japanese ships off Rondo island, about 23 miles (37 km) to the north-west of Sabang, and sank them in a gunfire and torpedo attack. The tank landing ship was in fact an auxiliary vessel of about 1,500 tons.
While retiring to the west after this attack, the destroyers came under sporadic bombing attack by a few aircraft, but suffered neither damage nor casualties. All the ships subsequently returned to harbour, Penn departing the Batu islands group on 14 June and Paladin during the afternoon of the following day.