Walsh joined the
King's Royal Rifle Corps as a rifleman in 1944 and was commissioned in 1945. He spent the winter of 1945–46 in northern Italy guarding against incursion by
Josip Broz Tito's partisans. After instructing at the Small Arms School and the Jungle Warfare School in
Malaya, he was seconded to the 3rd Battalion of the
Parachute Regiment (known as "3 Para") and went with it to
Cyprus in 1956 as a company commander, where he took part in operations against
EOKA insurgents. In November 1956, the
Suez Crisis had come to a head and 3 Para was tasked with capturing
El Gamil airfield close to
Port Said – part of
Operation Musketeer. This was the first and last British operational parachute assault since the Second World War. Despite fierce opposition including tanks, the airfield was captured in 30 minutes. After various staff and training appointments, he returned to the role of company commander with 3 Para to take part in the 1964 campaign in the
Radfan Mountains in
Saudi Arabia. After promotion to
lieutenant colonel, he took command of 1 Para on an emergency tour to
Aden in January 1967. The battalion was responsible for "Area North" for seven months and were the last British battalion to withdraw. Walsh was awarded the
Distinguished Service Order for various actions in June. The citation reads: "By his outstanding devotion to duty, personal bravery and exceptional powers of command, Lieutenant-Colonel Walsh contained the situation at
Sheikh Othman whilst never departing from the principle of minimum force." Walsh then held staff appointments with
British Army of the Rhine (BAOR) and the
28th ANZUK Infantry Brigade in Singapore. He was appointed Assistant Chief of Staff, Intelligence in 1973. Following promotion to
major general he took command of
3rd Armoured Division in 1976 and was then appointed Director of Army Training in 1978, retiring in 1981. ==Retirement years==