The Tone-class (利根型巡洋艦) were the last heavy cruisers completed for the Imperial Japanese Navy. They were supposed to be the 5th and 6th vessels in the Mogami-class, until the IJN notice the 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 hangar. Thus giving them a very distinctive silhouette, which allowed for strong and compact protection of the magazines while also increasing and improving the living quarters aft.