of the turbines to 80% of maximum power during peacetime. The ships had a length of about overall. They had a beam of and a draft of . They displaced at standard load. Their crew ranged from 1,187 to 1,224 officers and enlisted men. Both ships were fitted with a pair of Mitsubishi-Curtis geared steam turbine sets with a total of , each driving a propeller. Steam was provided by six water-tube boilers; Jun'yō had Mitsubishi three-drum boilers that operated at a pressure of and temperature of while Hiyō had Kawasaki-LaMont boilers. Their machinery, designed for merchant service, was over four times heavier than that of the purpose-built aircraft carrier . The ships had a designed speed of 25.5 knots, but both exceeded that by small margins during their sea trials. They carried of fuel oil which gave them a range of or more at . Flight deck arrangements The flight deck was long and had a maximum width of . A large island was fitted on the starboard side that, for the first time in a Japanese carrier, was integrated with the ship's funnel. This was angled 26° outwards to help keep its exhaust from interfering with flight operations. The ships were designed with two superimposed hangars, each approximately long, wide and high. Each hangar could be subdivided by four fire curtains and they were fitted with fire fighting foam dispensers on each side. The hangars were served by two square elevators with rounded corners, on each side. The elevators had a maximum capacity of and took 15 seconds to go from the lower hangar to the flight deck. The ships were fitted with electrically operated Kure type model 4 arresting gear with nine cables. They also mounted two Type 3 crash barricades. No aircraft catapult was fitted. The ships mounted a crane on the port side of the flight deck, just aft of the rear elevator. When collapsed, it was flush with the flight deck. Their air group was originally intended to consist of 12 Mitsubishi A5M "Claude" fighters, plus 4 in storage, 18 Aichi D3A "Val" dive bombers, with an additional 2 in reserve, and 18 Nakajima B5N "Kate" torpedo bombers. This was revised to substitute a dozen Mitsubishi A6M Zero fighters, plus 3 in storage, for the A5Ms by the time the ships were commissioned in 1942. As a result of the lessons learned from the