Tone-class cruiser

Tone-class heavy cruiser
Class overview
Name:	Tone class
Operators:	Imperial Japanese Navy
Preceded by:	Mogami class
Succeeded by:	none (Ibuki class not completed)
Completed:	2
Lost:	1
General characteristics
Type:	Heavy cruiser
Displacement:	11,213 tons (11,392 tonnes) (standard load) 15,200 tons (15,443 tonnes) (full load)
Length:	189.1 m (620 ft 5 in)
Beam:	19.4 m (63 ft 8 in)
Draught:	6.2 m (20 ft 4 in)
Propulsion:	4 shaft Gihon geared turbines 8 boilers 152,000 shp (113,000 kW)
Speed:	35 knots (65 km/h; 40 mph)
Range:	8,000 nautical miles (15,000 km; 9,200 mi) at 18 knots (33 km/h; 21 mph)
Armament:	8 × 203 mm guns (4 x 2) 8 × 127 mm guns (4 x 2), 12 × 25 mm Type 96 AA guns (6 x 2) 12 × 610 mm torpedo tubes (4 x 3)
Armour:	100 mm (3.9 in) (belt) 65–30 mm (2.6–1.2 in) (deck)
Aircraft carried:	6 x floatplanes
Aviation facilities:	2 catapults

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 hangar. 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. The Tone and the Chikuma were intended to provide the long range reconnaissance needed for Japan's carrier Air Fleets.

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 155 mm (6 in) turrets, three forward and two aft. However, the capsizing 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 (8 in) guns in four twin turrets with maximum 55-degree elevation, as was installed on the Mogami-class vessels. No. 1 was forward firing, No. 3 and No. 4 turrets trained through after arcs, while No. 2 was on a superfiring pedestal mounting overlooking No.1 and No.3.