The two Tone-class cruisers (利根型巡洋艦, Tone-gata jun'yōkan) were the last heavy cruisers completed for the Imperial Japanese Navy. The Tone-class cruisers were originally envisaged as the 5th and 6th vessels in the Mogami class. However, by the time construction began, serious weaknesses in the Mogami-class hull design had become clear following the Fourth Fleet incident in 1935. As Japan no longer was obligated to abide by the limitations of the London Naval Treaty, a new design was created and new means of construction were utilized. Though the external dimensions were close to the Mogami class, the design was quite different, with all the main battery of guns placed forward of the bridge, reserving the entire stern area as a large seaplane operations deck. Unlike the U.S. Navy, the Japanese did not have a dual role attack/scout aircraft, nor did they assign any of their carrier aircraft to a reconnaissance role. Little emphasis was placed on this aspect of carrier warfare. Instead the Japanese reserved all of their carrier aircraft for attack roles. Reconnaissance then was relegated to the float planes carried by cruisers.^[2] The Tone and the Chikuma were intended to provide the long range reconnaissance needed for Japan's carrier Air Fleets.