During the interwar period Bucknall served initially with his old battalion in Germany, the Egyptian Army. He then returned to the 1st Middlesex and remained with the battalion until he attended the Staff College, Camberley from 1928 to 1929. His fellow students there included John Harding, Gerald Templer, Richard McCreery, Gordon MacMillan and Alexander Galloway. After returning to his regiment he was made a GSO3 at the War Office from 21 January 1931, until 30 August 1932, when he returned to the Royal Military College, Sandhurst, to command a company of gentlemen cadets. Bucknall was promoted to brevet lieutenant colonel on 1 January 1936, and attended the Royal Naval College, Greenwich. From 13 March 1937until 12 April 1939 he served as an instructor at the Royal Military College of Canada, taking over from Gordon MacMillan, where he came into contact with some of the Canadian generals of the next war, such as Harry Crerar, the college Commandant, and E. L. M. Burns and Guy Simonds, both fellow instructors. He returned to the United Kingdom in 1939 and became CO of the 2nd Battalion, Middlesex Regiment. He was only with the battalion for a few short months, however, before receiving promotion to colonel on 1 August and being made an Assistant Quartermaster-General at the War Office.
Bucknall was still in this post by the outbreak of the Second World War, in September 1939, by the time the British Expeditionary Force left for France. He then commanded the 138th Infantry Brigade and, promoted to acting major general on 29 July 1941, was appointed General Officer Commanding53rd Infantry Division. His rank of major general was made temporary on 29 July 1942. He was promoted to the acting rank of lieutenant general on 12 September 1942 and succeeded Lieutenant General John Crocker as GOC XI Corps in East Anglia. He held this command until April 1943 when he succeeded Lieutenant General Frederick Morgan as GOC of I Corps, which was earmarked as an assault formation for the invasion of Normandy. With the 3rd Canadian Division and the British 3rd and 49th Infantry Divisions, along with, under command, I Corps. He was made a Companion of the Order of the Bath on 2 June 1943. Frustrated at training troops and wishing to command troops in battle in an overseas theatre of war, he requested demotion in rank, to temporary major general, so he could command a division. Sent to the Mediterranean, his chance came on 3 August 1943 when he was ordered to be GOC of the 5th Infantry Division during the final stages of the Allied invasion of Sicily. He later led the division during the Allied invasion of Italy and in the early stages of the Italian Campaign. His rank of major general was made permanent on 21 December 1943. Bucknall impressed General Sir Bernard Montgomery, the 21st Army Group commander, and when he was chosen to command Operation Overlord, the Allied invasion of Normandy, he appointed Bucknall to command XXX Corps – Bucknall took command on 27 January 1944, and was made an acting lieutenant general. On 11 March his rank of lieutenant general was made temporary. However, the Chief of the Imperial General Staff, General Sir Alan Brooke believed Bucknall to be unsuitable for command at that level. By August 1944 Bucknall was removed from his command, due to the relatively poor performance of XXX Corps, to be replaced by Lieutenant General Brian Horrocks. Montgomery conceded that it had been a mistake to appoint him and, in November 1944, Bucknall revert to his permanent rank of major general and was given command of Northern Ireland, a post he held until his retirement from the army on 4 March 1948. He was granted the honorary rank of lieutenant general.
Postwar
In 1952 Bucknall was given the colonelcy of the Middlesex Regiment, a position he held until 1959. He died at the age of 86 on 7 December 1980 in a nursing home in Chegworth.
