A century ago, Japan's land was mostly submerged due to catastrophic tectonic plate shifts. Now, however, the country has re-emerged as a maritime powerhouse, boasting state-of-the-art coastal cities, efficient sea routes, and impenetrable naval defenses. As a result, the marine industry is thriving, and young girls are inspired to become Blue Mermaids; an elite group of skilled women who are committed to safeguarding the oceans. At Yokosuka Girls' Marine High School, two childhood friends, Akeno Misaki and Moeka China, reunite after a lengthy separation. Along with other girls who share their passion for becoming Blue Mermaids, they embark on rigorous training exercises. Akeno and Moeka take on formidable responsibilities as captain and crew, respectively, aboard the Harekaze, a destroyer ship. Unfortunately, an unanticipated malfunction in the engine and navigation system leaves them stranded and exposed to grave danger. The anime series, High School Fleet, follows the courageous crew of the Harekaze as they navigate treacherous waters and surmount adversities they encounter along their path to becoming full-fledged Blue Mermaids.