In June 1937 he was promoted to captain and the following year joined the naval staff at the Admiralty, in the Tactical Division. In May 1939, a few months before the outbreak of the Second World War, he became deputy director of the Training and Staff Duties Division. In October 1940 he was given command of a
Dido-class light cruiser, , then under construction on the
Clyde. The ship worked up at Scapa Flow and as part of the Second Cruiser Squadron took part in
the May 1941 hunt for the Bismarck. The ship was then assigned to Force H based at Gibraltar on convoy duties to
relieve Malta. The ship rammed the
Italian 600-Serie Adua-class submarine near
Tunis on 2 July 1941, for which Oliver was awarded a
Distinguished Service Order (DSO) in November. In 1942 the ship was part of the force which captured the Vichy French island of
Madagascar after which it was assigned to Admiral Sir
Henry Harwood's Eastern Mediterranean fleet. In June 1942 as part of the 15th Cruiser Squadron the cruiser took part in
Operation Vigorous, an attempt to supply Malta with a convoy dispatched from the Eastern Mediterranean whilst another Malta-bound convoy was simultaneously dispatched from Gibraltar (
Operation Harpoon). On 15 June, Operation Vigorous was abandoned because of the strength of the air attacks, the depletion of ammunition and fuel caused by them and the nearby presence of the Italian Fleet. The convoy turned away from Malta and headed back towards Alexandria, but early the following morning
Hermione was torpedoed and sunk by south of Crete with the loss of 87 crew out of 570. Oliver survived the sinking and served as naval liaison officer to the Nile Delta Army for the next few months, until October 1942 when he was promoted to Commodore 2nd Class and assigned in
Gibraltar to organise shipping for
Operation Torch, the invasion of French North Africa. Following the successful invasion, in January 1943 he was assigned as the senior officer of the North Africa Inshore Squadron, based at
Bone, Algeria which at that time was under repeated air attack, until May 1943 when he moved to a newly captured base at
Bizerte. For his work during Operation Torch, Oliver was awarded a
Bar to his DSO and American
Legion of Merit. In July 1943 he became commander of Force "N", with its headquarters at the
Algiers naval base , for
Operation Husky, the invasion of
Sicily which took place on 9 July. He was the naval commander of the British assault force at
Salerno on . Following the successful conclusion of the operation he was appointed a
Companion of the Order of the Bath and upgraded to a Commander of the American Legion of Merit. From late 1943 until February 1944 he was the chairman of a commission, "Accuracy of Gunnery Committee". He was then promoted to commodore 1st Class and assigned as commander of Force "J" for
Operation Neptune, the invasion of Normandy, for which he was awarded a second Bar to his DSO. From October 1944 until February 1945 he was in command of the
First Aircraft Carrier Squadron on , part of the Eastern Fleet, clearing mines in the
Aegean Sea and providing humanitarian relief. He was promoted to
rear admiral in May 1945 when the force was attached to the Eastern Fleet's
21st Aircraft Carrier Squadron where it took part in the amphibious landing at Rangoon. When
Japan surrendered in August 1945 the force was preparing for the attack on the Malay Peninsula. ==Postwar==