Shinkai no Kantai: Submarine 707  

Deep Sea : Mission Mû, 深海の艦隊 サブマリン707, Undersea Fleet Submarine 707F

A strange item attacks and destroys any vessel on water. The submarine 707 is tasked with finding this mysterious object when summoned by a whale. Following the whale's lead, they arrive in the realm of Mu. However, upon their journey, they encounter the mysterious object, which turns out to be Commander Red Silver, who sought Mus magma sources for his own gain. The submarine engages in battle against Red Silver to protect Mu and safeguard the world from harm.