Tension between India and Pakistan had steadily escalated over the years, culminating on 1 September 1965 in a massive attack in the Chhamb sector by Pakistani forces. Possessing the initiative in having chosen the time and place to strike and enjoying overwhelming numerical superiority in the sector in both armour and troops, Pakistan posed a grave threat to Indian forces on the ground and so, in response to urgent requests for air strikes against Pakistani armour advancing in the Chhamb-Jaurian sector, Vampire FBMk.52s of No. 45 Squadron, at the time undergoing operational training at a forward base, mounted their first sorties at 1745 hours on the first day of the conflict, and on their heels came the Mysteres of Nos.3 and 31 Squadrons operating from Pathankot. The Pakistani armoured thrust was staggered. IAF Gnats proved their mettle in shooting down PAF Sabres in this sector, the first of aerial victories being notched by Nos. 23 and 9 Squadrons. Rapidly escalating, full scale warfare broke out on 6 September all along the international border between West Pakistan and India.
In the days that followed, IAF Canberras raided the major PAF bases at Sargodha and Chaklala at night, flying 200 counter air and interdiction missions against these and other Pakistani bases, including those at Akwal, Peshawar, Kohat, ChakJhumra and Risalwala. The virtuosity of the Hunters was fully demonstrated, Nos. 7, 20 and 27 Squadrons being employed in counter-air as well as interdiction and close air support missions in the West while Hunters of No. 14 Squadron battled with Sabres of the PAF No. 14 squadron raiding the IAF base at Kalaikunda in the East. The Mysteres were employed primarily in the ground attack role in which they proved extremely effective, with their swaths of 5 5 mm rockets most effective against armoured vehicles. Perhaps the most outstanding operational success was enjoyed by the Gnat, the three squadrons of which provided the air defence mainstay by flying CAPs over most operational IAF bases as well as fulfilling escort missions. Indeed, such was its success particularly against the F-86, that it was to earn the appellation of "Sabre Slayer". The September conflict was the first full-scale war in which the post-independence IAF was involved and the Service learned many lessons as a result. Post mortem examination revealed some requirements, the pace of expansion being slowed while lessons were digested. It was realised that too much emphasis had been placed on quantity at some cost in quality in order to cater for the dictates of the very high tempo IAF expansion embarked upon following the Sino-Indian War. This had necessitated cutting the duration of training courses to maximise personnel output and there was evidence that this could have some adverse effect on operational efficiency.. Emphasis was now reversed in that quality once more took precedence over quantity and training underwent major reorganization in consequence.