was the second vessel completed of the four-member of heavy cruisers of the Imperial Japanese Navy (IJN), which were active in World War II. The other ships of the class were , , and . She was named after a mountain in Wakayama Prefecture.
Background
The Myōkō class was approved under the 1922–1929 Fleet Modernization Program as the first heavy cruisers to be built by Japan within the design constraints imposed by the Washington Naval Treaty, and was the first of the "10,000-ton" cruisers built by any nation. Naval architect Vice Admiral Yuzuru Hiraga was able to keep the design from becoming dangerously top-heavy in its early years by continually rejecting demands from the IJN general staff for additional equipment to the upper decks. During modifications and rebuildings in the 1930s, though, the final displacement rose to 15,933 tons, well over the treaty limits.
Design
The Myōkō class displaced , with a hull design based on an enlarged version of the . Nachi was long, with a beam of and draft of , and was capable of 35.5 knots.
In December 1937, Nachi underwent her second modernization program at Sasebo Naval Arsenal, doubling the number of torpedoes to 16, adding another eight Type 96 25-mm antiaircraft guns and bulges to the hull to improve stability.
Later that same evening, Nachi and Haguro tracked down the allied force again and closed to 16,000 yards, firing their torpedo batteries. A torpedo from Nachi struck the Dutch light cruiser , blowing up her 5.9-inch (15 cm) magazines, tearing the cruiser in two as it sank in two minutes. Several minutes later a torpedo from Haguro hit the light cruiser , resulting in the cruiser sinking to progressive flooding over nearly three hours, and killing Admiral Karel Doorman.
thumb|Nachi, Haguro, Myōkō, and Ashigara anchored in Beppu, 1930
Two days later, on 1 March, Nachi and Haguro and their accompanying destroyers spotted the crippled Exeter as she attempted to escape the Java Sea, and joined forced with the cruisers Myōkō and Ashigara (and their accompanying destroyers). The four cruisers hit Exeter with shells that disabled her electrical power and guns, set her aflame, and destroyed her remaining boilers, leaving her dead in the water, leading to the allied cruiser's scuttling via her own crew. Nachi then retreated alongside Haguro, while Myōkō and Ashigara both engaged the destroyer , which they overpowered and sank. The destroyer , which was accompanying the two British ships, initially escaped the melee only to be caught and crippled about two hours later by planes from the Japanese light carrier Ryūjō, and finished off by Myōkō and Ashigara.
Operations in northern waters
Later in March, Nachi received a refit at Sasebo for operations in northern waters, and patrolled the Kurile Islands in April and May. On 26 May, Nachi departed from Ōminato Guard District as flagship of Vice Admiral Boshiro Hosogaya's force for the invasion of the Aleutian islands, and patrolled south of Attu, returning to Ōminato on 23 June. She departed Ōminato to escort another convoy to Kiska from 28 June, remaining in the Aleutian Islands until 7 July. After a refit at Yokosuka Naval Arsenal from 14–30 July, Nachi was reassigned to the IJN 5th Fleet with and . She continued patrols of the Kurile Islands though March 1943, and was sent as an escort for a reinforcement convoy to Attu from 7–10 March. Of the crew, 807 were lost, including the captain, while 220 survived and were rescued by the destroyers and .
Wreck
In April and May 1945, divers from made 296 dives on the wreck, salvaging radar equipment, code books, and maps of Japanese fortifications on Luzon and other documents. John Prados, in his book, Combined Fleet Decoded, writes that this was a major intelligence coup. This is also verified by U.S. Navy Master Diver Joseph S. Karneke, who served as the master diver aboard Chanticleer while diving on the wreck of Nachi, in his book, Navy Diver.