He joined the Defence Force in 1948 and served as an artilleryman in 4 Field Training Regiment and 14 Field Regiment. As a major, he completed the British Army Command and Staff course in 1960. Chief Instructor at the School of Artillery and Armour. Officer Commanding 14 Field Regiment at Bethlehem until 1967. Col Roos was appointed as the Military Attaché in Portugal during 1969 to 1971. Second in Command and Commander Divisional Artillery at Headquarters 7 Division. He was in command of the management team in Angola during the "Bridge 14" operation circa 1974 during the cold-war era power vacuum left by the Portuguese evacuation. OC Western Province Command. He was retained on Reserve List of Officers and served as officer in charge of National Key-points for the South African Defence Force over period 1977-1992. He was appointed as an Honorary Colonel of The Cape Town Rifles (Dukes) between 1991 and 1992.
He was recruited by the Royal Dutch Shell Oil company at retirement from the Army to the position of Chief of Security South Africa, where he served the remainder of his life espousing the principle of "being the harder nut to crack". He succumbed to prostate cancer in 2 Military hospital in 1992.
Notes
^Only the Cunene clasp was awarded, to members who served in Angola during Operation Savannah in 1975 and 1976. Recipients of the clasp wear a button, with the letter C encircled by a wreath, on the ribbon bar.
^Grandfathered. Long Gunnery Course, Larkhill, Great Britain. Number is assigned for convenience.