In the Pacific Ocean, an international naval fleet at Pearl Harbor engages in a dynamic and intense series of war games. Elsewhere, NASA scientists have discovered an extrasolar planet similar to Earth with conditions that could support life. In an attempt to communicate with potential inhabitants of this newfound world, they send a powerful signal from a communications array in Hawaii. Alex Hopper, a talented but undisciplined slacker, joins the Navy at the behest of his brother, Commander Stone Hopper, in an effort to turn his life around. During the exercises, Hopper is aboard the destroyer USS John Paul Jones, while his brother commands the USS Sampson. Complicating matters further, Alex is in a relationship with Samantha Shane, the daughter of the fleet's admiral, Admiral Shane, which adds tension to his military career and personal life.

Unbeknownst to the fleet and the rest of humanity, the signal sent by NASA reaches the alien planet and is answered—not with a message, but with an alien armada. The extraterrestrial ships splash down in the waters near Hawaii, erecting a massive energy dome that isolates a portion of the fleet, including the John Paul Jones and the Sampson. When the alien invaders launch an attack that decimates several ships including the Sampson, it becomes clear that Earth is facing an unprecedented threat. As the extraterrestrial onslaught intensifies, Hopper must step up to fill his brother's shoes and lead his crew against an enemy unlike any they've faced before.