IJN Agano Class Light Cruisers
The Agano class was designed as a swift and lightly armored lead vessel for destroyer squadrons. Four ships were laid down in the class, the Agano, Noshiro, the Yahagi, and the Sakawa. With the exception of the Agano, which sunk in February, 1944, all the ships received upgrades in their anti-aircraft weaponary by March, 1944, and again in July of the same year.
The Yahagi was sunk by hits from bombs and torpedos while a part of the suicide run by the Yamato in April, 1945. The Agano was sunk by the American submarine Skate, while her sister ship the Noshiro was sunk during a retreat from the Battle of Samar by carrier borne aircraft. Only the Sakawa survived the war, and she was used as a test subject in the Bikini Atoll atomic tests in 1946.
Sakawa was a welded steel cruiser of the Agano class. Particulars of the ship are not fully documented since Japanese records were destroyed at the time of the surrender. The U.S. Navy's official report on the Japanese Navy, ONI-221-J, issued in June 1945, cites a length of 550 feet overall and a beam of 49.6 feet. The vessel's length is not cited in other sources; its sister ship Yahagi, built at the same yard at roughly the same time, had a length of 531 feet between perpendiculars. Sakawa displaced 6,652 tons. The ship had a flush deck, "with marked sheer to the forecastle." The Agano class cruisers were also fitted with bulbous bows. The four shafts were driven by steam turbines; steam was provided by six Kanpon boilers. Agano was rated at 10,000 shaft horsepower at 35 knots; Sakawa probably had the same rating. The vessels were reportedly armed with six 6-inch/50 caliber guns, paired in three turrets, two forward and one aft. Sakawa had an antiaircraft battery of four 3.1-inch/65 caliber guns, and thirty-two 25mm/65 caliber Hotchkiss guns. Sakawa also mounted eight 24-inch torpedo tubes above water and carried 16 depth charges. Each Agano class cruiser also carried two floatplanes for observation, launched from a single catapult.
The cruiser Sakawa was built at Sasebo Navy Yard for the Imperial Japanese Navy as part of that nation's 1939 Programme of Naval Construction. Fourth and last of the Agano class cruisers, Sakawa and its sisters were the first regular light cruisers to be added to the Imperial Japanese Navy in more than ten years. Laid down in 1942, Sakawa was launched on April 9, 1944, and completed on November 30 of the same year. Sakawa was the only vessel of its class to survive the war. Intended for use as flagships for destroyer flotillas, the Aganos were lost in combat. Agano was sunk by USS Skate off Truk on February 17, 1944; Noshiro was sunk by carrier aircraft from USS Hornet and Wasp on October 26, 1944; Yahagi was sunk while sortying with the battleship Yamato on April 7, 1945. The undamaged Sakawa was at the Japanese naval base at Maizaru (on the coastline of the Sea of Japan) in August 1945. After use as a reparations vessel, Sakawa was selected as a target ship for Operation Crossroads. Sakawa sailed to Bikini from Yokosuka in company with the battleship Nagato. Both vessels were readied for the tests at Bikini by a U.S. Navy repair ship. This work included removing the airplane catapults, torpedo tubes, 6-inch guns, and smaller gun mounts from the cruiser.
Sakawa was moored off the port quarter of Nevada. The actual detonation of the Able bomb took place some 490 yards above and slightly to starboard of Sakawa's stern. Following the blast, observers noted that Sakawa's superstructure and hull had suffered major damage. The superstructure aft of the bridge was smashed down, as was the stack, which collapsed forward. The mainmast toppled forward and to port until it overhung the side by one-third of its length. Reports also noted that "the tops of the after mounts were crushed. The tops of the forward mounts were dished in a fore and aft V having a two-foot maximum depression." The worse damage, however, was to the hull. "The stern was most badly damaged.... Its deck plating was crushed inward and shell plating about the counter was twisted and torn open in several places. Shell plating on the starboard side...was badly wrinkled from approximately frame 145 aft." Other damage included the dislodging of deck fittings, the smashing of the lifeboats, and a fire that broke out on the stern and raged for two hours.
Immediately after the test Sakawa's stern sank two feet. Through the night the stern continued to settle as the cruiser listed to port. Some 24 hours after the test, the ship lay on its port beam, half submerged, with the stern on the lagoon bottom. Sakawa's bow sank beneath the lagoon surface at 10:43 a.m. on July 2. According to the U.S. Navy, "flooding unquestionably started when the Sakawa's stern was ripped open to the sea by the blast....Poor watertight integrity...permitted progressive flooding. After 24.5 hours the main deck was awash. In the next hour rapid progressive flooding, probably due to poorly fitted and damaged hatches, vent trunks, and other fittings in the main deck, sent the Sakawa to the bottom." At the time of sinking, the Navy tug Achomawi (ATT-148) had a line aboard Sakawa and was attempting to pull the ship from astern to shore; the cruiser was moved astern about 150 feet when it finally sank. The Navy was able to board and inspect the cruiser prior to sinking; "diving operations on this vessel were assigned low priority and eventually limited by a time factor to recovery of instruments. Hence no diver's report is available..."
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