Nobita and his friends under the waters of the Pacific Ocean. Gian and Suneo take Doraemon's underwater vehicle and travel through the Atlantic Ocean, trying to find a treasure ship. Along the way, they discover that the environment gun that Doraemon used to protect them is running out of energy leaving them vulnerable to the sea. Fortunately, they are rescued by some marine creatures.
Doraemon: Nobita and the Castle of the Undersea Devil (ドラえもん のび太の海底鬼岩城, Doraemon Nobita no Kaiteiki Ganjō) is a 1983 Japanese animated science fantasy film and the fourth Doraemon feature film, released on March 12, 1983, in Japan. Directed by Tsutomu Shibayama, the film is based on the Western myth of Atlantis, the lost city.