Robert Bruce Milligan was born on 16 June 1936 at Taree, New South Wales, and educated at Taree High School.

He joined the 13th National Service Training Battalion in January 1955, served with the 17/18th Infantry Battalion, CMF, (Citizens' Military Forces) from April 1955 to September 1957, 1 RTB (1 Recruit Training Battalion) from September 1957 to November 1957, 4 RAR from November 1957 to May 1958 and 2 RAR from May 1958 to January 1961. He applied for entry to OCS (Officer Cadet School) Portsea in October 1960 and was selected for entry in January 1961.

In December 1961, Colour Sergeant Milligan graduated from OCS Portsea as Dux of his Class, being awarded the Governor General's Medal, the Staff Prize, the Field Prize and the Skill at Arms Prize.

He was posted to PIR (Pacific Islands Regiment) as a Platoon Commander, ADC to the Commander of the 1st Division then 2iC of C Company, 5 RAR, on 24 January 1966.

On 13 February 1967, 5 RAR was taking part in Operation Beaumaris and tasked with a cordon and search of An Nhut, a village of approximately 1,000 people, about six kilometres southeast of the Australian Task Force base at Nui Dat.

At about 0900h on the following day the OC of C Company held an orders group. As the members left the group, a member triggered a large explosion from a well concealed mine, causing death and injury. Major Bourne, Captain Milligan and Captain Williams were killed outright and five other men were wounded.

Captain Milligan's remains were returned to Australia and he was buried at the Northern Suburbs Cemetery, Sydney, on 23 February 1967.