Tone class

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TONE 利根 class

The two Tone class cruisers were the last heavy cruisers produced for the Imperial japanese Navy. They participated in numerous actions during in World War II. The Tone class cruisers were originally envisaged as the 5th and 6th vessels in the Mogami class and were funded as such under the 2nd 1932 Supplementary Budget.These very vessels were intended to provide long-range air scouting for cruiser squadrons and to operate together with aircraft carrier task forces.

The Tone class cruisers had a very distinctive silhouette, with all main armament concentrated forward and the aft section entirely devoted to aircraft operations. This allowed for strong and compact protection of the magazines while also increasing and improving the living quarters aft.As originally planned, the Tone class vessels were to have five triple 152 mm turrets, three forward and two aft. However, the capsize of the torpedo boat Tomozuru called into question the stability of all Japanese warship designs. As a result of the redesign, and to improve accuracy of gunfire, all five turrets in the new design were concentrated on the forecastle. When Japan abrogated the Washington Naval Treaty on 31 December 1936, the main armament was revised to eight 203 mm guns in twin turrets with maximum 55 degree elevation, as was installed on the Mogami class vessels. No. 3 and No. 4 turrets trained through the after arcs, while No. 2 was pedestal mounted overlooking No.1 and No.3. Heavy anti-aircraft weaponry consisted of four twin 127 mm gun turrets in shielded mountings amidships. For close-range, six twin 25mm were carried. Four triple banks of 610 mm torpedo tubes were also incorporated.

The previous Mogami-class experimented with welded hulls, with limited success. Thus the lead vessel in the Tone-class, Tone, also had some welding, the subsequent Chikuma was an all riveted design. The undulating hull of earlier cruisers was dispensed with and the superstructure was less built-up. The modifications to the design raised the nominal displacement to about 12,500 tons. The main belt armor was 100 mm thick next to machinery spaces (125mm next to magazines), and it extended to a depth of about 9 feet, beyond which it had a much reduced thickness as an anti-torpedo bulkhead down to the inner double bottom.

The Tone class had no aircraft hangar, but there was a comprehensive arrangement of transport rails and turntables on the aircraft catapult and quarterdecks. Two gunpowder-propelled catapults were located on the beam abaft the mainmast. A maximum of four Kawanishi E7K2 'Alf' three-seat floatplanes and four Nakajima E8N1 'Dave' floatplanes could be carried, the normal complement being six, of which four were to be E8Nls. In practice, no more than five were ever embarked. As the war progressed these types were superseded by the Aichi E13A1 'Jake' and Mitsubishi F1M2 'Pete'.

In 1943, the number of 25 mm guns was increased to twenty guns, and in June 1944, when the opportunity to use their aircraft had passed, further mountings were added on the flight deck, bringing the light anti-aircraft total to 54 barrels. Two more twin 25 mm guns were also added later. Radar was fitted, but otherwise no major modifications were carried out.