He gained commission with the Pakistan Air Force (PAF) on 22 June 1963 in the 36th GD(P) Course with serial number PAK-4362, and being the Wing Under Officer, was a candidate for the Sword of Honour, but did not end up receiving it. In a debate at the PAF Academy in Risalpur, Karim passionately advocated for the Language Movement of 1952, which compelled the Government of Pakistan to establish Bengali as an official language on par with Urdu and English, which were the official and mainstream languages in West Pakistan. He was later nominated and became known as the captain of the basketball team at the academy. Flight Lt. Matiur Rahman (later recipient of the Bir Sreshtho in the 1971 Bangladesh Liberation War) and Air Vice-Marshal Momtaz Uddin Ahmed were his classmates in both Sargodha and Risalpur.