Lieutenant-General Sir Oliver William Hargreaves Leese, 3rd Baronet KCB CBE DSO (27 October 1894 – 22 January 1978) was a British general during the Second World War.

Leese was the first son of Sir William Hargreaves Leese, 2nd Baronet, a barrister, and was educated at Ludgrove and Eton. Early in the First World War, he joined the army and he was commissioned into the Coldstream Guards on 15 May 1915. Leese was wounded three times, the last during the Somme offensive in 1916, an action in which he was Mentioned in Despatches and awarded the DSO. The citation to his DSO which was gazetted in November 1916 read:

For conspicuous gallantry in action. He led the assault against a strongly held part of the enemy's line, which was stopping the whole attack. He personally accounted for many of the enemy and enabled the attack to proceed. He was wounded during the fight.

After the war, he remained in the army being promoted captain in 1921 and attended the Staff College, Camberley from 1927 to 1928. In November 1929 he was appointed as Brigade Major to 1st Infantry Brigade (Guards) and was formally promoted to major a few days later. He was promoted to brevet lieutenant-colonel in July 1933.

On 18 January 1933 Leese married a granddaughter of Sir Baldwyn Leighton, 8th Baronet, Margaret Alice (d. 1964), daughter of Cuthbert Leighton (recte Leicester-Warren), DL, JP, (1877-1954), of Tabley House, Knutsford, by Hilda Margaret Davenport; they had no children. Lady Leese's brother was the last of the line to own the Tabley estate which he left on his death in 1975 to the National Trust.

From 1932 to 1938 Leese held a number of staff appointments and was promoted to lieutenant-colonel in December 1936, brevet colonel in September 1938 and colonel in October 1938. In September 1938 he was posted to India to be a GSO1 instructor at the Staff College, Quetta. He had succeeded to the baronetcy on his father's death on 17 January 1937.

Second World War

Leese returned to the UK from India in March 1940. It had been planned for him to command a brigade in Norway but with the German invasion of Western Europe in May, he was sent to join Lord Gort's headquarters as Deputy Chief of Staff of the British Expeditionary Force. He evacuated from Dunkirk with Gort on 31 May

On his return to the UK Leese was ordered to form and train a large brigade group, 29th Infantry Brigade. In December 1940 he was appointed acting major-general and given command of the West Sussex County Division which included 29th Brigade. A month later he was moved to command of the 15th (Scottish) Division. His rank was upgraded to temporary major-general in November and was made substantive in December. In June 1941 he was given command of the Guards Armoured Division during its formation and training.

In September 1942 he was sent at the request of Eighth Army commander Bernard Montgomery to North Africa to assume command, as an acting lieutenant-general, of the Eighth Army's XXX Corps. Montgomery had formed a good opinion of Leese when he had instructed him at Staff College in 1927 and 1928 and had also been impressed by his work at GHQ in France.

Leese commanded the Corps for the rest of the campaign which ended with the Axis surrender in May 1943 in Tunisia. He was mentioned in despatches for his services in North Africa.

The Corps then took part in the Allied invasion of Sicily in July 1943 before returning to the UK after the Sicily campaign, which ended in August, to prepare for the planned invasion of Northwest Europe. Leese was promoted to temporary lieutenant-general in September.

On 24 December 1943, however, Leese received a telegram ordering him to Italy to succeed Montgomery as Eighth Army commander as Montgomery was to return to the UK in January 1944 to prepare for the Allied invasion of Normandy. Leese commanded the Eighth Army at the fourth and final Battle of Monte Cassino in May 1944 (when the bulk of the army was switched in secret from the Adriatic coast to Cassino to strike a joint blow with the United States Fifth Army) and for Operation Olive on the Gothic Line later in 1944. His rank of lieutenant-general was made permanent in July 1944.

In September 1944 he was appointed to succeed George Giffard as the Commander-in-Chief of Eleventh Army Group and assumed command in November, by which time the Army Group had been renamed Allied Land Forces, South-East Asia. He viewed the existing command structure as inefficient and proceeded to appoint former members of his Eighth Army staff. The methods of the two staffs differed and the newcomers were resented. As Slim expressed it in his memoirs, "His staff, which he brought with him... had a good deal of desert sand in its shoes, and was rather inclined to thrust Eighth Army down our throats."

Leese's command covered three separate groups: the Northern Combat Area Command under US Lieutenant General Dan Sultan, Fourteenth Army under Lieutenant-General William ("Bill") Slim in central Burma and finally, further south in the Arakan, Indian XV Corps under Lieutenant-General Philip Christison. Through the year-end he fought a successful campaign which led to the capture of Rangoon by an amphibious landing (Operation Dracula) in early May 1945.

Slim had turned Fourteenth Army into an effective military force and had commanded a highly successful campaign from the relief of Imphal to the recapture of Rangoon including the destruction of the Japanese forces in Burma. However, Leese believed that Slim was very tired (he had asked for leave once Rangoon had been taken) and proposed to the Supreme Commander South East Asia, Louis Mountbatten and the CIGS, Alan Brooke, that he should be replaced by Philip Christison (who had amphibious experience and so would be well suited to leading the army in the planned seaborne landings in Malaya), leaving Slim to take over the new Twelfth Army with the less demanding task of mopping up in Burma. Leese misread the reactions of Brooke and Mountbatten and having then met Slim to discuss the proposals came away believing Slim had agreed to them. In fact, Slim reacted by telling his staff he had been sacked and wrote to Leese and Claude Auchinleck, the C-in-C India, to say he would refuse the new post and resign from the army in protest. Once the news circulated within the Fourteenth Army, mutinies and mass resignations of officers were threatened.

Leese was obliged to reinstate Slim when the Supreme Commander South East Asia Louis Mountbatten, although he had authorised the original proposals, now refused to support him. Mountbatten subsequently approached Alan Brooke (who had always doubted Leese's suitability for the role) and they agreed that Leese should be removed. He was succeeded by Slim.

Post-war

None of the main parties' actions in the Slim affair show up well in retrospect. Richard Mead in Churchill's Lions suggests that Leese was naive, Slim petulant and Mountbatten devious. However, it was Leese's career that suffered and he returned to the UK to be GOC-in-C Eastern Command, a significant downward move having been one of only three army group commanders in the British Army. His promotion to full general is believed to have been blocked by Mountbatten and he retired from the army in January 1947 and became a noted horticulturist, writing books on cacti and keeping a well noted garden at his house, Lower Hall in Worfield, Shropshire. Although a keen cricketer, he had only modest success as a batsman in the 1914 Eton XI and was relegated to 12th man for that year's Eton v Harrow match, but was President of the Marylebone Cricket Club in 1965. He served as High Sheriff of Shropshire in 1958.

Following amputation of his right leg in 1973, Leese moved into Wales into a house called Dolwen at LLanrhaeadr-ym-Mochnant, near Oswestry. He died there after a heart attack on 22 January 1978, aged 83, and was buried at Worfield parish church.