OZMA is a science fiction anime series set in a dystopian future on a mostly-barren Earth. Though with only six episodes and about two total hours screen time, it's really more like a movie than a series.
The protagonist is Sam, a stereotypical brash-but-good-at-heart kid who is trying to measure up to the memory of his brother by pursuing the sand whale Ozma. In the process, he comes across Maya, an Ideal Child running from her siblings in the Theseus Army. Together with Sam's shipmates on the sandship Baldanos, they evade the Army, pursue Ozma, and eventually transform the world.
OZMA uses a good amount of submarine combat - well, actually, "sub-sand" combat - complete with torpedoes, active sonar pings, and depth charges. A good portion of several episodes is taken up with some tense hide-and-seek games between the Baldanos and Theseus Army ships. It's fairly well done, once you get past the quantum drive plot device that allows it all to happen.
By the end of the series, it's pretty clear that the story is a parable of sorts, warning against trying to use science to take the place of nature. The genetic manipulation that led to the Ideal Children is a failure, both because their bodies are breaking down and because they're unable to adapt to changing conditions as well as the Natura. Maya uses Ozma to restore the biodiversity of the Earth, effectively ensuring the end of the poorly-adapting genetically modified Ideal Children. The Natura survive, but are cautioned to live in harmony with the planet rather than dominate it.
OZMA isn't a particularly deep story, though it certainly does have a message. Regardless of how you feel about that, it's still a decently entertaining way to spend a couple of hours.