Boshirō Hosogaya was born on 24 June 1888 to a farming family in Nozawa, in Nagano Prefecture, in the mountains of central Japan. He went from that rural start to the Imperial Japanese Naval Academy at Etajima, where he graduated with the 36th class in 1908, sixteenth of 191 cadets.
His early years at sea followed the usual path for a promising young officer. As a midshipman he served in the cruiser Soya and the battleship Kashima. After his commission as ensign he went through the torpedo and naval artillery schools. As a sub-lieutenant he served in the destroyer Asagiri and the battleship Suwo. He completed the 18th class of the Naval War College, and in the early 1920s he served on the Navy General Staff. After the Great Kantō earthquake of 1923 he also served at the martial-law headquarters for the Kantō region, where the navy helped restore order in a ruined Tokyo and Yokohama.
He was promoted to commander in 1924 and became executive officer of the cruiser Yūbari. In 1927 and 1928 he travelled in the United States and Europe, and in 1928 he became executive officer of the battleship Hyūga. After his promotion to captain in 1929 he served as executive officer and then captain of the heavy cruiser Chōkai. In 1934 he took command of the battleship Mutsu, one of the two most powerful ships in the fleet. He was made rear admiral on 15 November 1935 and ran the Communications and Torpedo Schools during 1935 and 1936. He became vice admiral on 15 November 1939 and took over the Ryojun (Port Arthur) Guard District. A year later he commanded the 1st China Expeditionary Fleet.
On 25 July 1941 Hosogaya became commander in chief of the Fifth Fleet, based at Ōminato. It was a northern command, mostly administrative, responsible for the waters off Hokkaidō, Karafuto and the Kuril Islands, and it had only light cruisers and other light forces. In June 1942, as part of the Midway operation, he directed the Aleutian campaign: the carrier raid on Dutch Harbor and the occupation of Attu and Kiska.
His name is tied above all to the Battle of the Komandorski Islands on 26 March 1943. Flying his flag in the heavy cruiser Nachi, he was escorting transports carrying reinforcements to Kiska. He had two heavy cruisers, two light cruisers and four destroyers when he met a smaller American force under Rear Admiral Charles McMorris: one heavy cruiser, Salt Lake City, one light cruiser and four destroyers. The gun battle lasted for hours in the cold northern sea, and Salt Lake City was badly hurt. But Hosogaya mistook the splashes of American dye-loaded shells for bomb splashes, concluded that aircraft were attacking him, broke off the action and turned back, taking the convoy with him.
In Japan the retreat from a weaker enemy was seen as a failure of nerve. He lost his command to Shirō Kawase and was moved to the reserve later in 1943. For the rest of the war he was at Truk as Governor of the South Seas Mandate, the last man to hold that office, from 1943 to 1945, while the American advance cut the islands off one after another.
Hosogaya survived the war and died on 8 February 1964.
Sources
Wikipedia, "Boshirō Hosogaya" (citing Dull, A Battle History of the Imperial Japanese Navy; Lorelli, The Battle of the Komandorski Islands; Morison, vol. 7; Nishida, Imperial Japanese Navy).
Live Pacific Ships page for this officer (Komandorski, flag in Nachi).