Commander Samuel Dealey cautiously guides his Gatoclass submarine USS Harder through the tropical night along the surface of the Sibutu Passage, the treacherous waters that separate Borneo from the Philippines. It is June 6, 1944, and the area is infamously rife with Japanese destroyers. But Harder isn’t deterred; on the contrary, that’s why she’s here. Along with several transport and cargo ships, she already has one destroyer under her belt, and she’s on the hunt for more.

Suddenly, a lookout's voice cuts through the saltladen air to announce the presence of an enemy convoy on the horizon. On Dealey’s orders, Harder surges forward, but luck isn't on their side. As the moon bathes the sea in silver light, the submarine is exposed. One of the destroyers, alerted to the danger, wheels around, charging straight for them. Harder plunges beneath the waves, but the enemy ship continues bearing down on her position.

Through the periscope, Dealey watches the destroyer grow larger by the second. It’s now or never. Three torpedoes erupt from Harder's tubes, streaking through the water towards their target. Suddenly, two massive explosions rock the sea. Through the periscope, Dealey watches in awe as the destroyer, now identified as Minazuki, breaks in half and slips beneath the waves in mere minutes.

There’s no time to celebrate the second destroyer is already moving in, hellbent on avenging Minazuki. Harder has drawn first blood, but the battle is far from over…