Tenzan-class battleship

Each ship displaced 72,000 tons at full load, and the class were the second-heaviest battleships ever constructed. In addition, the class carried nine 460mm naval guns capable of firing 1,460 kg shells over 42 km. These remain the second-largest naval artillery to ever be fitted on warships, only surpassed by the 510mm guns of the battleship Oyashima.

All four ships were highly active during the Second Escar-Varunan War, participating in many fleet actions. Three ships were sunk by the Chiseian Royal Navy, while the Tenzan herself was sunk by land-based aircraft from Chanha.

Background
During the early 20th century, Yamatai's ultranationalist and expansionist ideology sought to completely dominate and annex Chisei and its colonial empire, and a confrontation between the Imperial Navy and Royal Navy was considered inevitable. The Yashima-class battleships were designed in accordance to the Imperial Navy's primary naval strategy at the time, shaped by their prior experience in the First Escar-Varunan War. This strategy called for a single "decisive battle" to be fought between the Imperial Navy and the Chiseian Royal Navy in order to decide the outcome of a naval war between the nations, with battleships taking centre stage to destroy the Royal Navy's forces.

In 1925, Chisei and Yamatai signed the Mikawa Conventions, which aimed to limit the growth of their naval forces in order to attempt to avoid another major confrontation between the states. Under the Conventions, both countries agreed to halt capital ship construction for 10 years and to commit to a total tonnage limitation of 315,000 tons. The signing of the Wanshu Conventions was highly unpopular with the Imperial Navy, though they had not been able to oppose the signing partly due to ongoing power struggles within the Yamataian military government at the time. Design work on a new post-war class of battleships continued without regard for the limitations imposed by the Conventions.

The Royal Navy was still numerically superior to the Imperial Navy after the Yamataian victory in the First Escar-Varunan War, and their large colonial empire enabled them to maintain such large numbers even after the defeat, prompting the Imperial Navy to attempt to build a class of battleships individually superior and far surpassing anything Chisei or foreign competitors had built. In June 1929, the first two Yashima-class battleships were laid down in secrecy, ostensibly as a civilian project to circumvent the Wanshu Conventions. Subsequently, the Chiseian Royal Navy also laid down the aircraft carrier Bakekujira with similar explanations in early 1930, signalling that the Wanshu Conventions had been abandoned by both countries. From 1930 onwards, both countries dropped any pretense and re-intensified their naval arms race until the start of the Second Escar-Varunan War.

Tenzan
Tenzan was sunk during the Battle of the Qieli Strait, the first engagement between the Yamatai Imperial Navy and the Chanhan Navy once Chanha declared war on Yamatai. During the battle, she was attacked by over 280 land-based aircraft from Chanha. Tenzan was hit by four torpedoes and six bombs before finally sinking.

Tateyama
Tateyama was the second ship to be launched. During the Allied invasion of Hinomoto, she carried out a suicidal attack to disrupt the Allied landing convoys, after which she was intentionally beached near Akakiri in order to become a stationary anti-aircraft and coastal artillery platform. She provided artillery support during the Battle of Akakiri, but eventually ran out of ammunition and was ultimately overrun by Chiseian troops. Following the war, the wreck of Tateyama was a popular attraction amongst the occupation soldiers for a time before she was demolished and taken apart for scrap by the Chseian Occupational Government in 1952 due to safety concerns.

Ontakezan
Ontakezan was the first of the Tenzan-class battleships to be sunk. On 27 February 1939, she was attacked by carrier aircraft in the Crosswind Sea while moving to support land operations on Imoshima and was sunk by several hits from bombs and torpedoes. This was a major propaganda victory for Chisei and its allies, and the sinking of the ship was heavily suppressed in Yamatai to the point that sailors' families were not informed of their deaths until after the loss of the Tenzan eight months later.

Yakushizan
Yakushizan was sunk by several Royal Navy submarines in the Varunan Ocean while carrying out solo convoy-raiding operations.

Cultural significance
The Tenzan-class battleships have carried a notable presence in Yamataian culture since the time of their construction to the present day, matched only by the prestige of the Oyashima. Upon completion, the battleships represented the epitome of Imperialist Yamataian naval engineering, and were seen as a strong symbol of Yamataian national pride at the time. Due to their immense size, speed, and power, the ships embodied Yamatai's determination to defend its interests and reunite the Yashiman people under the ideology of Pan-Yashimanism.