Nippon Oil Corporation Akita Refinery

Nippon Oil, founded in Niigata Prefecture in 1888, was Japan's first modern oil company and built refineries in the oil-producing regions of Niigata, Akita and Hokkaido. The Nippon Oil Corporation Akita Refinery (日本石油秋田製油所) was established at Tsuchizaki Port, Akita Prefecture, on the northern waterfront next to the harbour and railway, taking advantage of the rich Akita oil fields — Japan's most productive domestic petroleum source. Output from the Yabase field, developed in earnest in the 1930s, rose rapidly, and Japanese sources state that it at one time supplied more than 70 percent of domestic crude.

Japan depended overwhelmingly on imported oil, and domestic crude met only a small part of demand. After the oil embargo of 1941 the military and government counted on seizing the oil fields of the Dutch East Indies while pressing domestic fields for maximum output. Akita crude was refined at Nippon Oil's Tsuchizaki works and at Nippon Mining's Funakawa refinery on the Oga Peninsula. During the war, the refinery was a vital facility for producing aviation fuel and other petroleum products essential to the Japanese military, and as the sea lanes from the south were cut from 1944 it was described as one of the largest oil installations in Japan.

Its strategic importance made it a high-priority target for the USAAF 315th Bombardment Wing, based on Guam, which specialized in radar night attacks on Japanese petroleum infrastructure; Tsuchizaki was the last target of that campaign. From about 10:30 p.m. on August 14 to about 3:30 a.m. on August 15, 1945, more than 130 B-29s (sources give between 100 and 140) dropped some 12,047 bombs. The refinery was completely destroyed in the Tsuchizaki Air Raid, and bombs also fell on nearby housing and the port. It was one of the last American air raids on the Japanese home islands, ending about half a day before the Emperor's surrender broadcast.

The dead included refinery workers and their families, local residents and soldiers. The exact toll is unknown: it is usually given as more than 250, while other counts give 92 or 184. The refinery was rebuilt after the war and the site is now ENEOS's Akita oil terminal, while output from the Akita fields gradually declined. Tsuchizaki has a memorial to the victims and preserves part of a bombed refinery building; the Tsuchizaki Port Air Raid Museum, opened in 2018, displays these remains and survivors' testimony.