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These ships were designed in the late 1930s as replacements for the ageing 5,500-ton cruisers. As originally conceived they were to be armed with 6.1in guns in triple turrets and carry six 24in torpedo tubes. They were to have a high speed, with minimal protection. After a change in the staff requirements the design was reworked and they emerged as fast scouts, and were used in practice in the role of destroyer leaders. To this end, X turret was sacrificed for a heavier torpedo battery (quadruple banks in lieu of triple) and an aircraft installation.
The hull was flush-decked with a bulbous bow, and the armour was limited to a 56mm belt in the way of the machinery spaces, with 50mm protecting the magazines. Deck protection was 18mm and the turrets merely had splinter protection.
The machinery was a quadruple-shaft geared turbine arrangement with six boilers, developing 100,000shp for a maximum speed of 25kts. Like Yubari, but unlike any other cruisers since, the class had only a single funnel.
As completed, the main armament was the 152mm (6in) gun which had originally been put into service for the Kongo class battlecruiser. Stock guns were subsequently then used to arm the Agano class. This gun, developed from a 50cm Vickers weapon, fired a 100lb projectile and had a range of 22,970yd. The twin turrets, manufactured at Sasebo, allowed a maximum elevation of 55° and could thus be used for barrage AA fire. Secondary armament consisted of four 80mm HA, which were actually 3in (76.2mm) in two twin mountings. These 60cal weapons fired a 13.2lb projectile (fixed ammunition), and were the only such guns afloat in the IJN. Thirty-two 25m completed the AA outfit, reflecting war experience, which had clearly shown the threat from aircraft attack. The torpedo tubes were mounted on the centreline according to destroyer practice, and given a rapid reload system for the eight spare torpedoes. The aircraft fittings included a single catapult on the centreline forward of the main mast, and stowage for two floatplanes on a platform over the tubes. As with destroyers, depth charge equipment was fitted in these ships.
Four ships were provided for under the 1939 4th Replenishment Programme, three being ordered from Sasebo and one from Yokosuka. Only the name ship was completed with any despatch, so their active service lives were limited because Japan's fortunes had by then declined.
Modifications
Light AA was increased to 46 25mm by 1944, and in the surviving ships thereafter to 52 and then 61 25mm (10 x 3, 31 x 1) by July 1944. Radar was fitted at completion, except perhaps in Agano.
Service
Agano served as leader of the 4th Destroyer Flotilla after entering service and, with her flotilla, participated in the final battles for Guadalcanal during the first couple of months of 1943. In October that year the flotilla was transferred to Rabaul for operations in the Solomon Islands, and after the US landings on Bougainville was committed to attack the invasion force on the night of 1/2 November. The Japanese force of four cruisers and six destroyers encountered the US TF39 (four cruisers and eight destroyers) and was routed, Agano escaping with minor damage. However, a few days later, on 5 November, Agano was badly damaged in Rabaul harbour by aircraft from Saratoga and Princeton, and in a subsequent attack by aircraft from TF38 on 11 November she received a torpedo hit as well. Ordered to home waters for repair after makeshift repairs at Truk, the cruiser was torpedoed and sunk some 160nm north of that island by the US submarine Skate on 16 February.
Noshiro was at Truk in November 1945 with the 2nd Destroyer Flotilla, and was also ordered to Rabaul for operations in the Solomon Islands theatre. She, too, received damage during the US carrier aircraft raids on Rabaul harbour on 5 November. After repairs at Truk she transported troops to Rabaul and Kavieng in December, being slightly damaged by air attacks on her return trip to Truk on 1 January 1944. She served in the Marianas in the summer of 1944, sailing in June with Yamato and Musashi to cover the transport of reinforcements to Biak, and was part of Admiral Kurita's force during the Battle of the Philippine Sea between 18 and 22 June. At the Battle of Leyte Gulf in October 1944 Noshiro was part of the Centre Force with her destroyers, and took part in the battle off Samar, but on the withdrawal was sunk west of Panay on the morning of 26 October by aircraft from Wasp and Hornet.
Yahagi assumed the role of leader of the 10th Destroyer Flotilla, seeing action in the Marianas in May/June 1944. During the Battle of the Philippine Sea she was part of Carrier Group A, and during the Battle of Leyte Gulf she, too, was with Kurita's Centre Force with the 10th destroyer Flotilla. After the US invasion of Okinawa on 1 April 1945, the remnants of the Imperial Japanese Navy were ordered to attack the invasion zone, despite the critical shortage of fuel which meant that it would be a one-way trip for the flagship Yamato. Yahagi sailed with this force from the Inland Sea, but the vessels were caught by US carrier aircraft in the East China Sea and annihilated. Yahagi was hit by some seven torpedoes, six claimed by aeroplanes from Langley alone, as well as a dozen bombs, and sank on the afternoon of 7 April 1945.
The last ship, Sakawa, was not completed until the end of 1944, by which time there was little fuel available to the IJN. As a result she never became operational and survived the war unscathed, despite the heavy carrier raids on Japanese bases in the last months of the war. After the war she was used as a repatriation ship, and was then expended in the atom bomb tests at Bikini Atoll in 1946.
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