Pre-war doctrine held that the ship's own firepower, rather than its aircraft, were to be relied upon for protection, since in the absence of radar, fighters were unlikely to intercept incoming attackers before they could release their weapons. Accordingly, the Illustrious class was given an extremely heavy Anti-Aircraft armament. The armament was similar to "Ark Royal" with twin 4.5 inch turrets (in a new "between-decks" or countersunk design) arranged on the points of a quadrant. The guns were mounted sufficiently high so that they could fire across the decks; de-fuelled aircraft would be stowed in the hangar for protection during aerial attack. The "Illustrious Class" were fitted with four HACS controlled High Angle Director Towers, for fire control of her 4.5" guns. "Illustrious" pioneered the use of Radar to vector carrier borne fighters onto attacking or shadowing aircraft, and a Fairey Fulmar fighter from "Illustrious" achieved the first radar directed kill on 2 September 1940.