The Tone class was to improve upon the Mogami class of cruisers. The Tone class were ordered under the 2nd 1932 Supplementary Program / 2nd Reinforcement Program of 1934.
The Tone class were intended to be used as scouting cruisers so they were designed to have a large area aft that could be used to handle the aircraft they were intended to carry.
There was more electric welding used to try and keep the weight down in the Tone. However, because of strength problems found during typhoons, the Chikuma used more riveting to help strengthen the hull.
With the main guns forward that left the quarterdeck to be used for aircraft. This allowed for all guns to be fired while launching aircraft without possibly damaging the aircraft.
There were two gunpowder propelled catapults to launch aircraft.
The Tone class was designed to carry four E7K2 "Alf" and four E8N1 "Dave" floatplanes but only five were ever carried. As World War II went on E13A1 "Jakes" and F1M2 "Pete" replaced them.
As the Japanese had cancelled the naval treaties on December 31, 1936, the Tone class were upgraded to have 8" guns during construction. All of the turrets were mounted forward of the bridge.
The torpedo launchers were located near the catapults.