Ships
- IJN Chokai Captain from 19 October 1940
Seishichi Watanabe was born on 22 February 1893 in Fukuoka Prefecture. After Fukuoka Prefectural Shuyukan Middle School he sat the examinations for both the Naval Academy and the Army Academy, and he entered the navy. He graduated with the Naval Academy's 42nd class on 19 December 1914, standing 56th in a class of 117, and went to sea as a midshipman in the cruiser Aso. In 1915 he shifted to the battleship Hizen and was commissioned ensign that December. Service in the battleship Kirishima followed. From December 1917, as a lieutenant junior grade, he took the basic gunnery and torpedo courses and then served in the destroyer Oite.
Promoted lieutenant on 1 December 1920, he completed the navigator course at the Naval College. His sea duty then ran through the destroyers Urakaze and Namikaze, the transport Takasaki, the oiler Kamoi, and the light cruisers Yahagi and Naka. He became a lieutenant commander in December 1926, served in the cruiser Asama, and from December 1929 taught at the Naval Academy. In the early 1930s he was navigator of the battleships Ise and Mutsu. Promoted commander on 1 December 1932, he instructed at the Gunnery School and the Navigation School and also taught at the Naval College. In December 1936 he became executive officer of the heavy cruiser Ashigara.
He was promoted captain on 1 December 1937 while commanding the oiler Erimo. In December 1938 he took the light cruiser Kinu, and in November 1939 the submarine tender Jingei. On 19 October 1940 he became captain of the heavy cruiser Chokai. The Takao-class ship had spent the late 1930s as a flagship on the China coast, and through 1941 she worked up for war. Late that November she became flagship of Vice Admiral Jisaburo Ozawa's First Southern Expeditionary Fleet and moved to Hainan.
From Hainan, Chokai covered the December 1941 landings in northern Malaya. When the Royal Navy's Force Z put to sea, Ozawa's ships sortied to find it. Land-based aircraft sank Prince of Wales and Repulse before the cruisers closed the British force, and Chokai returned to Cam Ranh Bay with those ships unengaged. In January and February 1942 she supported the seizures of Borneo and other points in the Dutch East Indies. On 22 February, while maneuvering off Cape St. Jacques, she grounded on an uncharted reef. She came off with her speed reduced and went into Singapore for emergency repairs.
By early April she was at sea again with Ozawa for the raid into the Indian Ocean. In the Bay of Bengal on 6 April 1942, Chokai and the ships in company are credited with the American freighter Bienville and the British steamers Ganges and Selma City. Watanabe brought the cruiser home later that month and left her on 25 April 1942. Gunichi Mikawa, who had commanded the same ship as a captain in the mid-1930s, later flew his flag in her as commander of the Eighth Fleet, including at Savo Island. Kosaku Aruga was among the captains who followed. Chokai was lost on 25 October 1944 in the battle off Samar while Jo Tanaka was in command.
Watanabe next managed Sasebo harbor, from 10 May 1942. In January 1943 he joined the staff of the Third Southern Expeditionary Fleet. He was promoted rear admiral on 1 May 1943, and that July he took the Kure Local Defense Squadron. In December he became chief of the third section of the Hydrographic Department. When that office was set up on its own in April 1944 as the Navy Ministry's Weather Division, he was its first director.
On 10 April 1945 he received the 104th Escort Squadron and spent the last months of the war on convoy duty. He left active service on 20 September 1945. Watanabe died on 15 February 1948.