Warship Island, also known as "Battleship Island", is one of the anime-only places visited in the Warship Island Arc. The island, which is in the shape of a battleship, is where the Sennenryu, a thought-to-be extinct race of dragons that live for 1000 years, come to die and be reborn.
The Dragon's Nest is an area found underneath Warship Island. It rises from the ocean every 1000 years, during which time the Sennenryu gather to give birth and die.
The island may have been based on a real Japanese island, as there two places in Japan nicknamed "Gunkanjima", or "Battleship Island". Hashima Island got this nickname from its apparent resemblance to a battleship, which caused the US Navy to torpedo it during World War II [1]. Mitsukejima also got this nickname because of its shape.