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.