The first operational Lightning, designated "Lightning F.1", was designed as an interceptor to defend the V Force airfields in conjunction with the V Force airfield's own "last ditch" Bristol Bloodhound missile defences from enemy nuclear-armed bomber attack long enough for the also nuclear-armed V Force bombers to take-off and get clear of their airfields which, along with the dispersal airfields, would be the highest priority targets in the UK for enemy nuclear weapons. To best perform this intercept mission, emphasis was placed on rate-of-climb, acceleration, and speed, rather than range – originally a radius of operation of from the V bomber airfields was specified – and combat endurance. It was equipped with two 30 mm ADEN cannon in front of the cockpit windscreen and an interchangeable fuselage weapons pack containing either an additional two ADEN cannon, 48 unguided air-to-air rockets, or two de Havilland Firestreak air-to-air missiles; a heavy loadout optimised for damaging large aircraft. The Ferranti AI.23 onboard radar provided missile guidance and ranging, as well as search and track functions.