After serving in HMS Furious from 3 January 1938, Oliver Patch joined 824 Squadron in HMS Eagle on 1 September 1938 and was in that squadron at the outbreak of war. Eagle was at that time completing a short refit at Singapore and she was then employed hunting for surface raiders and blockade runners in the Indian Ocean. Unfortunately on 14 March 1940 a 250lb bomb detonated as it was being fused, killing thirteen ratings, and as a result the ship spent a further seven weeks out of action at Singapore.

Eagle then transferred to the Mediterranean in May 1940. On 10 June 1940 Italy entered the war and from then onwards Eagle's aircraft were busy attacking Italian shipping and covering convoys. On 9 July 1940 the Italian Fleet was encountered off Calabria and 824 Squadron made two attacks but without much success. 824 Squadron then flew ashore and moved to Sidi Barrani and carried out a moonlight torpedo raid on Tobruk harbour on 20 July. The destroyers Nembo and Ostro were sunk in this attack.

On 22 August 1940, Captain Patch who was at RNAS Dekheila was sent to Ma'aten Bagush to take command of a sub-flight of three Swordfish which were standing by for a raid in Bomba Bay where a submarine depot ship had been sighted. The three aircraft armed with torpedoes flew to Sidi Barani at 7 am where the crews had an al fresco breakfast of tinned sausages and baked beans, with bread plastered with marmalade which had to be dug out of a 4lb tin with the breadknife. A dawn reconnaissance confirmed that the enemy shipping was still in Bomba Bay and at 10.30 am the sub-flight took off and headed out to sea led by Captain Patch. Flying low, they shaped a course 50 miles from the coast to avoid enemy fighters. At 12.30 they turned inshore into Bomba Bay and opened out to about 200 yards apart. Four miles from shore a submarine was sighted on the surface apparently battery charging. Patch immediately attacked, dropping his torpedo from a height of 30 feet at a range of 300 yards. This hit below the conning tower and the submarine sank. This was later confirmed as the Iride which had on board a team of frogmen who were intended to attack the British Fleet in Alexandria harbour with limpet mines. In the meantime the other two aircraft flown by Lieutenants Cheesman and Wenham, both RN, flew on to attack the inshore vessels which proved to be a depot ship and a submarine with a detroyer between them. The ships opened fire damaging one of the Swordfish, but the pilots dropped their torpedoes which hit their target causing a fire. This apparently reached the magazine of the depot ship which blew up and sank. Later RAF reconnaissance indicated that all three ships had sunk so that the sub-flight appeared to have sunk four ships with three torpedoes. This was admitted by the Italians and Admiral Cunningham wrote of this as a "phenominal result" and the attack as "brilliantly conceived and gallantly executed". Although an official booklet issued by the Ministry of Information in 1945, and at least five histories written by competent authors, all give the above version, recent research suggests that the submarine and destroyer were able to put to sea and were not sunk as at first thought. For this exploit Captain Patch was awarded the DSO, and the other aircrews were also decorated.
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The squadron then re-embarked in Eagle and in September they made a strike on Rhodes, but four aircraft were shot down by Fiat CR 42 fighters. Attacks were also made in this period on airfields, and harbours were mined. Patch was Mentioned in Dispatches on 16 September 1940 but details are not known but it was presumably in connection with these operations.
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In the meantime, on 1 September, HMS Illustrious had arrived in the Mediterranean and plans were made to attack the Italian Fleet in Taranto harbour. After delays caused by a fire aboard Illustrious,and defects in the petrol system of the Eagle, the raid was laid on for the night of 11 November 1940. The Eagle was still out of action so five of her Swordfish were transferred to Illustrious. One of these was E4F flown by Captain Patch. The first strike force of 12 Swordfish was made up of six armed with torpedoes, four with bombs and two with flares and bombs. Course was set at 2057 and the distance to the target was 170 miles. The torpedo aircraft went in first and it was then the turn of the bombers of which Patch was one. He attacked from 1500 feet against the cruisers and destroyers, dropping his bombs as he came over the cruisers at mast level. The second strike force, consisting of nine Swordfish, followed in half an hour and went into attack through the same terrifying hail of fire which had met the first attack. All but two of the total raiding force returned to the Illustrious, one crew being taken prisoner and the other killed. The results of this epic raid are well documented in almost every naval history book covering the Second WorJd War. For his part in the raid Patch was awarded the DSC, having been awarded the DSO only four months earlier.
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In March 1941 Patch joined a training squadron at Crail before being appointed to 816 Squadron in command. This squadron was employed in mine-laying and anti-shipping operations off the Dutch coast but details are not known. On 17 June 1944 he was appointed to HMS Thane as Commander (Flying) and joined her at Norfolk, Virginia. The ship was earmarked to be an assault fighter carrier but her first two trips were to ferry aircraft from the USA to Capetown, and then from Norfolk to Glasgow with another batch of 55 aircraft. She then ferried more aircraft to Abadya in the Red Sea but on her next trip from New York to the Clyde she was damaged in the approaches to the Clyde by a torpedo from U482 on 15 January 1945.
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Major Patch was then transferred to HMS Trumpeter, taking over as Commander (F) from Major Newson. This ship saw more operational service than any other CVF and took part in thirteen offensive operations between August 1944 and May 1945. Whilst Patch was Commander (F) Trumpeter also took part in Convoy JW65 to Russia, but no action took place until approaching Kola when two ships were sunk by U boats. These were the last losses on the Russian run. Major Patch returned to Corps Duty on 29 March 1945 and served in 46,44 and 40 Commandos and TTC before returning to sea as SRMO in Theseus.

He retired at his own request on 1 September 1955.