Doraemon: Nobita's Great Mermaid Naval Battle is an anime film that premiered in winter 2010.

About the production: the story comes from a manga, the film runs about 99 minutes and its current status is "finished".

Its main genres are comedy, with themes such as Kids and Mermaid.

On AniList, Doraemon: Nobita's Great Mermaid Naval Battle has an average score of 69%, a good score, and appears on 2,800 users' lists.

Nobita asks Doraemon to take him somewhere they can dive and as a result the robot-cat uses several gadgets to make it possible for both to able to swim on an imaginary ocean above sea level. Inadvertently a mermaid ends up on Nobita's backyard when they turn off the illusion. Her name is Sophia and she is a princess of an ancient underwater civilization. Doraemon, Nobita, Shizuka, Jyaian, and Suneo quickly become her friends and are invited to visit her homeland. While heading towards the underwater kingdom they find themselves amid a conflict between the mermaids and an opposing tribe that has driven them away from their home planet thousands of years ago. Doraemon, Nobita, and their friends must then aid Sophia find a legendary sword that might bring peace once again to the seas. (Source: Anime News Network)

Official synopsis from AniList.