When he was a captain in the Australian Army, Robertson was wounded during the capture of Tobruk from Italian forces. After this incident, Robertson was posted in Greece to fight against German forces. Later in New Guinea, by now promoted to the rank of lieutenant colonel and filling a senior liaison officer role, Robertson was ordered to inspect the US Army perimeter at Buna. Robertson was unsatisfied with what he saw, and reported his observations to General Edmund Herring, and General Richard K. Sutherland who was also present at the time. Consequently, Douglas MacArthur made changes to the US Army command at Buna. In August 1943, Robertson was again promoted, this time to the position of General Staff Officer Grade 1 to George Vasey, and Commanding Officer of the 7th AIF Division. During the Salamaua-Lae campaign, Vasey sent Robertson to Port Moresby to seek better relations with the US Army, and his manner was said to have surprised both the USAAF's General George Kenney and General Frank Berryman. Robertson later wrote to Vasey that he had succeeded in his task. Robertson, as Vasey's senior staff officer, was later involved in an operation following the capture of a Japanese order document. During World War II, Robertson served in Europe with the 51st Infantry Division, a British Army formation, in March 1944. He was then sent to the 50th Infantry Division, another British Army formation, while the division was engaged in the Battle of Normandy.
On becoming informed of a CIA operation in Chile in February 1973 which involved ASIS, the then Labor Prime Minister Gough Whitlam signed a document ordering the closure of ASIS operations in Chile. It appears, however, that ASIS agents did not leave Chile until October 1973, after the CIA-backed 1973 Chilean coup d'état had brought down the Allende Government. Whitlam accused Robertson of disobeying instructions by delaying the closure of the ASIS station in Chile. In the lead up to Indonesia’s invasion of East Timor in 1975, ASIS paid a Dili-based Australian businessman Frank Favaro for information on local political developments. The leaking of his identity in late 1975 led to another confrontation between Whitlam and Robertson. These incidents led to Whitlam sacking Robertson on 21 October 1975, with effect on 7 November, just 4 days before Whitlam's own dismissal in the 1975 Australian constitutional crisis, although Robertson disputes the reason for his dismissal in documents lodged with the National Archives in 2009.
