Yamataian battleship Oyashima

Named after the Yashiman archipelago, Oyashima was designed after the earlier Tenzan-class battleships, and was initially intended to be the lead ship in a four-ship class that would complement the Tenzan-class battleships. Keeping with Imperial Navy design philosophy at the time, Oyashima was intended to be qualitatively superior to the battleships of the numerically superior Chiseian Royal Navy, which was Yamatai's main rival in the Escar-Varunan region. She was laid down at Shirada Naval Arsenal in 1936 and formally commissioned at the height of the Second Escar-Varunan War in December 1940.

Throughout the rest of the war, she served as the flagship of the Imperial Navy. Oyashima participated in the Battle of the Qieli Strait, the only time where she saw combat and fired her main guns at enemy vessels. During the battle, she was attacked by the same land-based Chanhan aircraft that sank the Tenzan-class battleship Tenzan and sustained a torpedo hit, necessitating repairs at Shirada. After this, Oyashima rarely left Yamataian waters, mainly patrolling the Sea of Yashima and spending time moored at Awara Naval Base, where she served as the headquarters for the Commander of the Central Fleet, Admiral Arasaka Eijiro.

Oyashima was instrumental during the Kōkyo Incident at the end of the war, when a group of Yamataian military leaders launched a coup and met with representatives from Chisei to negotiate an armistice. Oyashima was sent to meet with the Chiseian Royal Navy, and the Oyashima Armistice was signed as Oyashima entered Wanshu Bay, marking the cessation of hostilities between Yamatai and the Escaric Allies. After negotiations concluded, Oyashima returned to Yamatai, where she spent years moored at Awara Naval Base and fell into disrepair. Plans were made to scrap the vessel, but due to the immense cultural importance of the ship these were never acted upon.

In 1960, a group of veteran sailors who had served on Oyashima lobbied for the ship to be preserved as a museum dedicated to the Imperial Navy during the war, successfully raising donations from veteran sailors and supporters across the country. Oyashima was towed to Shirada in 1962, where she was placed in drydock to receive extensive repairs and restoration work. In 1965, she was permanently moored at the newly-constructed Battleship Oyashima Memorial, and was officially struck from the Imperial Navy's register in a special ceremony at the opening of the museum, which was attended by Empress Kiyono and Prime Minister Okudera Gunzo.

Cultural significance
Galactic Battleship Oyashima. Enough said.

In 2012, the Oyashima was featured in the film Resurrection of Oyashima.

In the video game Gokudo 6, a conspiracy is revealed alleging that a second Oyashima-class battleship, the Shikishima, was constructed in secret and hidden in the city of Onomichi until 2014, when the existence and revelation of the ship becomes a major plot twist.