He was commissioned into the Royal Indian Air Force (RIAF) as a pilot officer on 17 September 1945.

During the Indo-Pakistani War of 1965, although a "desk jockey" in Peshawar, he volunteered for and flew dangerous low, low-level, night-time strafing missions in old Harvards along the Grand Trunk Road between Lahore and Amritsar harassing Indian Army convoys.

[3] By 1969 he had risen through the ranks of squadron leader and wing commander, working in staff jobs in Kohat and Peshawar, after earlier being based at Mauripur.

In 1971, Air Commodore Callaghan was the PAF Chief Inspector, in charge of the verification of Pakistani claims of enemy aircraft kills.

Working closely with him was the then-United States air attache/adviser to the PAF, USAF Brigadier General Charles "Chuck" Yeager (the first man to break the sound barrier).