[2] After Wellington College, Willison came first in the army entrance exam and attended the Royal Military Academy, Woolwich, passing out top of his year and winning the Pollock Medal for the highest academic achievement of his term.
[2] He was in command of 17th Field Company, attached to the 3rd Divisional engineers and, during fighting at Bénouville on the evening of D-Day, he was seriously wounded[2] by shrapnel and did not return to service until the following August.
In March 1945, during the advance on Bremen, his company had to reopen a mined road and a demolished bridge through flooded low-lying lands, in preparation for an assault.
[2] Over the following several postwar years, Willison attended the Staff College, Camberley (where he was judged to be one of the most outstanding students),[2] served as brigade major with 1st Indian Infantry Brigade as part of the reoccupation force in Java,[2] served as a staff officer at HQ Malaya Command, posted to the War Office in London and took command of 16 Field Company, Royal Engineers, stationed in Egypt.
After a spell from 1955 to 1958 as an instructor at the Staff College, Camberley,[2] Willison was posted to Aden where he supported the Special Air Service's assistance to the Sultan of Oman in the Djebel Akhdar during a pro-Nasser rebellion.
[1] This unit was part of the Strategic reserve, with detachments in several trouble spots; this gave Willison additional international experience.