Yahagi

History

Yahagi (矢矧) was an Agano-class cruiser which served with the Imperial Japanese Navy (IJN) during World War II.

Design

Yahagi was the third member of the Agano-class light cruisers, which were designed after Japan formally abandoned the interwar naval treaties, and thus became limited in naval construction only by financial and industrial capacity. At this time, the series of ‘5,000-ton’ and ‘5,500-ton’ flotilla leaders (Tenryu through Sendai-classes) were seen as increasingly obsolete – the destroyers they were meant to lead were considerably faster, and the American destroyers they were meant to overpower were starting to look as though they could overpower the small cruisers. Their age and obsolescence necessitated their replacement starting in 1941. Starting in 1936, preliminary planning for the new cruisers dubbed the ‘Design No. C-39’ began. Basic requirements asked for a 5,000-ton, 36-knot cruiser capable of steaming 7,000 nm at 18 knots, with an armament of 2x3 15.5cm guns, 4x2 8cm and 3x2 25mm AA guns, and 2x4 61cm torpedo centerline mounts. At least one catapult and accompanying seaplane was required, as was protection of 100mm for the machinery spaces.

On 2 March 1938, the Navy Technical Department presented their incarnation of Design No. C-39. The design was significantly larger, and changed several elements. The main battery was to be situated in three twin mounts, the heavy AA guns cut in half, and the radius of action reduced by almost 1,000 nm. However, this was not satisfactory and the design was further modified. Finally, on 13 October 1939 the design was presented again, as Design No. C-41 – what would ultimately become the Agano-class.

As a ship designed in the wake of the Fourth Fleet Incident, the Agano-class was designed to have greater longitudinal hull strength than previous designs, with the result of almost the entire ship being constructed out of Ducol steel (a high-strength construction steel), except for the armored portions (which contributed to the strength of the hull), which was made out of CNC (Copper-Nichel-Chromium Steel). Overall, the hull was considered to be suitably strong and stable, something lacking in most Japanese interwar designs, and was a welcome change. The armor protection of the Agano-class followed the same philosophy as prior Japanese flotilla leaders – armored enough to resist the guns of American destroyers, and their potential flotilla leaders. The main armor belt protected the machinery spaces, and was 60mm thick. The space was closed off by 20mm transverse bulkheads, and the deck protection likewise was 20mm thick. The magazines had more narrow 55mm armor belts, and likewise shared 20mm bulkheads and armor decks. The gunhouses were armored with 25mm plates Ducol plates. Machinery was in five boiler rooms followed by three machinery rooms. Two boilers were fitted in the foremost boiler room, with the four boiler rooms aft (divided by a centerline bulkhead) each containing a single boiler. The forward two machinery rooms contained the port and starboard outboard turbine groups, while the aft machinery room contained boat inboard turbines. The six Kampon RO-GO three-drum boilers operated at 30 kg/cm2 and with superheating had a peak temperature of 350°C. The four turbines each output 25,000 shp, for a combined power of 100,000 shp and a resulting top speed of 35 knots.

The main armament of the Agano-class was composed of recycled Vickers 6”/50 Mark II, which had been used to arm the battlecruiser Kongo, with license-built versions arming future Japanese capital ships. Six were mounted in three twin gunhouses (lacking a rotating stalk, these were not true turrets). The guns had an elevation range of -5°/+55°, and fired 45.36 kg HE shells at a velocity of 850 m/s to a maximum range of 21,000 meters at +45°. Rate of fire was 5-6 rounds per minute. The heavy anti-aircraft battery was made up of four 8cm Type 98, 76mm in actuality, which fired a 5.99 kg shell at a velocity of 900 m/s. Maximum altitude was 9100 meters. Rate of fire was 25 rpm, but due to insufficient hoist capacity sustained rate of fire was only half of this. The light anti-aircraft battery of the class as designed was six 25mm/60 Type 96 in two triple mounts, but Yahagi had an extra four twin mounts fitted as completed, bringing her total up to fourteen guns. The 25mm AA guns fired 250 gram shells at a velocity of 900 m/s, with the maximum theoretical range and rate of fire being 6800 meters and 260 rpm. However, effective range was 2,000 meters and rate of fire 120 rpm. By far the most potent part of the armament was the torpedo battery – two Type 92 quadruple torpedo mounts, which utilized the infamous Type 93 61cm torpedo. The cruiser held sixteen torpedoes – half were in the tubes, and half in the quick-loading installations, able to load a torpedo on average within 20-30 minutes, but potentially as rapidly as 3-5 minutes. Fire control was controlled via Type 94 low-angle directors, with the aid of two 6-meter duplex coincidence rangefinders. One was installed near the director, the other atop turret No.2. These fed a Type 94 surface fire control computer, which was used to control the secondary batteries aboard battleships (for 14cm to 15.5cm guns). For control of the 8cm guns, a Type 94 high-angle director was used. As completed, Yahagi was equipped with a 21-Go surface search radar. In July of 1944, a 13-Go air search radar and a 22-Go surface search radar were fitted, which could also be used for rudimentary radar fire control measures (ranging only).

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  Yahagi off of Sasebo, Nagasaki in December 1943

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  Yahagi sinking

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  Light cruiser Yahagi under intense bomb and torpedo attack