originally intended to consist of 12 Mitsubishi A5M ("Claude") fighters, plus 4 in storage, 18 Aichi D3A "Val" dive bombers, plus 2 in reserve, and 18 Nakajima B5N "Kate" torpedo bombers. This was revised to substitute a dozen Mitsubishi A6M Zero fighters, together with 3 more in storage, for the A5Ms by the time the ship commissioned in 1942. As a result of the lessons learned from the Battle of Midway in June, the ship's fighter complement was strengthened to 21 Zeros, and the B5Ns were reduced to 9. By the end of the year, 6 more Zeros replaced an equal number of D3As, giving totals of 27 A6Ms, 12 D3As and 9 B5Ns. Although it was possible to fit all these aircraft into the hangars, 8 or 9 were usually stored on the flight deck to reduce cramping below decks. Armor, armament and sensors As a conversion from an ocean liner, the ship could not support much armor, although it had a double bottom. Two plates of Ducol steel, each thick, protected the sides of the ship's machinery spaces. The ship's aviation gasoline tanks and magazines were protected by one layer of Ducol steel. Her machinery spaces were further subdivided by transverse and longitudinal bulkheads to limit any flooding. The ship's primary armament consisted of a dozen 40-caliber Type 89 anti-aircraft (AA) guns in six twin-gun mounts on sponsons along the sides of the hull. Jun'yō was also initially equipped with eight triple mounts for 25 mm Type 96 light AA guns alongside the flight deck. In mid-1943, four more triple mounts were added and another four triple mounts in late 1943 and early 1944. Two of these last four mounts were mounted on the stern and the others were placed in front of and behind the island. A dozen single mounts were also added, some of which were portable and could be mounted on the flight deck. After the Battle of the Philippine Sea in June 1944, the ship's anti-aircraft armament was reinforced with three more triple mounts, two twin mounts and eighteen single mounts for the 25 mm Type 96 gun. These guns were supplemented by six 28-round AA rocket launchers. In October 1944, Jun'yō had a total of 91 Type 96 guns: 57 in nineteen triple mounts, 4 in two twin mounts, and 30 single mounts. Two Type 94 high-angle fire-control directors, one on each side