A concealed observation station and military artillery battery on Oshima Island are part of a series of coastal fortifications around Kitakyushu. They were first installed during the Meiji era (1868–1912) to protect the coastline from potential attacks by Russian and Chinese fleets. Many were dismantled after the Japanese victory in the Russo-Japanese War (1904–1905). Some fortifications were strengthened again in the 1930s, when Japanese forces were stationed in Manchuria.

The battery on Oshima was completed in 1936. It consisted of four concrete gun turrets, a concealed observation station, an ammunition depot, and a storage space for searchlights. During World War II, heavy artillery was installed, including four cannons with a range of about 20 kilometers. The cannons are no longer on the island, but visitors can walk around the circular concrete pits where they were mounted.

The observation station is a simple concrete bunker concealed in an artificial hill, with views of the sea. It was used to calculate the distance and speed of enemy ships. Visitors can walk through the station. On a clear day, it is possible to see Okinoshima, a sacred island worshipped since ancient times.

During the Russo-Japanese War, Japan and Russia engaged in a naval battle off the coast of Okinoshima, as the two sides fought over rival interests in Manchuria and Korea. The Naval Battle of the Sea of Japan was fought May 27, 1905, in the Tsushima Strait, with Japanese forces under the command of Admiral Togo Heihachiro (1848–1934). The Japanese navy destroyed two-thirds of the Russian fleet. Some of the Russian sailors killed during the battle were brought to Oshima to be buried. In 2013, a memorial to those who died on both sides was built near the battery ruins. Each year, participants from both countries visit the site to hold a memorial service.

The Tsushima Strait is close to the Sacred Island of Okinoshima. A priest who was stationed on Okinoshima at Okitsu-miya Shrine (one of three shrines known collectively as Munakata Taisha), witnessed the battle and recorded it in his journal. After the war, a compass from the flagship Mikasa was donated to Munakata Taisha by Admiral Togo Heihachiro to commemorate the victory. Visitors can see the compass at the Shimpokan Museum, in the precincts of Hetsu-miya Shrine at Munakata Taisha.

（This English-language text was created by the Japan Tourism Agency.）