[1] Demobilized in January 1947, Simpson spent four years working in various jobs in Australia and Papua New Guinea, before re-enlisting in the Army in 1951 to serve in the Korean War with the 3rd Battalion, Royal Australian Regiment.

[2] Simpson was posted to the 2nd Battalion, Royal Australian Regiment in January 1954, where he was promoted to sergeant in 1955, serving in Malaya from October 1955 for the next two years.

He was subsequently posted to 1st Special Air Service Company (SAS) in November 1957 and served with that unit until selected as one of the initial group members of the Australian Army Training Team Vietnam (AATTV) sent to assist South Vietnamese forces in July 1962.

[1] On 16 May 1966, Simpson left the army for a second time, but re-enlisted in Saigon a year later for his third period of service with the AATTV, during which he was awarded the Victoria Cross.

On 6 May 1969, in Kon Tum Province, Simpson rescued a wounded fellow warrant officer and carried out an unsuccessful attack on a strong enemy position.

He then returned to his company where, with complete disregard for his safety, he crawled forward to within ten metres of the enemy and threw grenades into their positions.

He then threw smoke grenades and, carrying a wounded platoon leader, covered the withdrawal of the company together with five indigenous soldiers.

Warrant Officer Simpson quickly organised two platoons of indigenous soldiers and several advisors and led them to the position of the contact.

The wounded were eventually moved out of the line of enemy fire, which all this time was directed at Warrant Officer Simpson from close range.

At the risk of almost certain death he made several attempts to move further forward towards his Battalion Commander's body but on each occasion he was stopped by heavy fire.