Ships
- IJN Natori Captain from 28 July 1941 · Relieved on 1 July 1942
- IJN Mogami Captain from 10 November 1942
Seigo Sasaki served as a captain in the Imperial Japanese Navy during the opening year of the Pacific War, first in a light cruiser that led destroyers into the southern campaigns and then in a heavy cruiser rebuilt after Midway.
He took command of the light cruiser Natori on 28 July 1941. Natori, a Nagara-class ship completed in the 1920s, was then serving as flagship of Destroyer Squadron 5. From that bridge Sasaki took the squadron into the first southern operations of the war. In December 1941 the squadron covered landings on northern Luzon. In January 1942 it supported the seizure of Tarakan and Balikpapan on Borneo. In February it moved with the invasion forces against Java, and later in the spring it operated in the waters of the Netherlands East Indies and the Philippines as the Japanese consolidated those gains. He was relieved of Natori on 1 July 1942.
On 10 November 1942 Sasaki became captain of the heavy cruiser Mogami. The ship had been badly damaged at Midway the previous June, when she collided with Mikuma while turning away from an American submarine contact and was then bombed. She spent months in the yards at Kure, where two of her after turrets were removed and a flight deck was fitted so that she could carry reconnaissance seaplanes. Sasaki brought her back to the fleet as that converted cruiser.
Under his command Mogami worked up and then returned to the Southwest Pacific. In February 1943 she was assigned to the Eighth Fleet at Rabaul. During the spring she took part in transport and reinforcement runs toward the northern Solomons and New Guinea. On the night of 5–6 July 1943 she was in the covering force for a troop movement into Kula Gulf. American cruisers and destroyers intercepted the Japanese column, and in the confused night action Mogami was hit by gunfire and a torpedo. Damage to her forward magazines and hull left her burning and down by the bow. She was later judged beyond economical repair in the forward area and was eventually lost as a fighting unit of the cruiser force.
Sasaki’s two recorded wartime commands therefore span the first drive south and the later struggle to hold the Solomons. On Natori he served alongside officers of the destroyer squadrons that opened the Philippines and East Indies campaigns, among them Kenzaburo Hara, Akira Sone, and Ichiro Aitoku. On Mogami he followed Ryo Toma, who had commanded the cruiser at Midway, and took the rebuilt ship back into combat in the Solomons.
The public record of his career is clearest in those two ships and those years. The dates of his commands fix him as the captain of Natori from 28 July 1941 until 1 July 1942, and as captain of Mogami from 10 November 1942 through her return to the Solomons and the night action in Kula Gulf.