Leonard Monk Isitt junior was educated at Mostyn House, Cheshire, England and Christchurch Boys' High School.

He had one brother, Willard Whitmore Isitt (1894–1916), who was a Rifleman in the New Zealand Rifle Brigade in World War I and was killed in France on 31 October 1916.

[1] After service in Egypt he then moved to the Western Front where he was wounded in the head during the New Zealand Division's participation in the Battle of Flers–Courcelette.

During his period he shot down a single enemy aircraft, before being transferred back to England to serve as a flying instructor.

Based at Abscon airfield he flew his first mission on 9 October when 10 aircraft attacked Mons railway station.

In 1919 Isitt, then a captain, was posted back to New Zealand where he was sent to Sockburn airfield to take care of the four aircraft and serve as commanding officer.

[6] In 1937, the RNZAF was made independent of the New Zealand Army and at that time Isitt was promoted to wing commander and appointed as the Air Member for Personnel.

In May 1942 Isitt was sent to London to establish the RNZAF's Overseas Headquarters, receiving a promotion to air commodore at the same time.

In addition to securing a significant role for his Air Force in the South Pacific,[1] Isitt represented New Zealand at conferences in London, Washington and Ottawa during World War II.