In 2005 NASA discovers an extra-solar planet, called Planet-G, with conditions similar to Earth and transmits a powerful signal from a communications array in Hawaii. Meanwhile slacker Alex Hopper (Taylor Kitsch) gets arrested while attempting to impress Samantha Shane (Brooklyn Decker), daughter of United States Pacific Fleet commander Admiral Terrance Shane (Liam Neeson).Stone Hopper, Alex's older brother and a Commander under Terrance, is infuriated at Alex's lack of motivation and forces Alex to join him in the United States Navy. By 2012, Alex is a lieutenant aboard the Arleigh Burke class destroyer USS John Paul Jones, while Stone is the commanding officer of USS Sampson. Alex is in a relationship with Samantha and due to disciplinary problems is in danger of being discharged from the Navy. Alex got nervous before asking for Sam's hand in marriage & picked up a fight with a naval officer from Japan, who had earlier kicked Alex in the face during a soccer match. Their ships, along with others from around the world, are taking part in RIMPAC naval exercises in Hawaii. Stone informs Alex that he will be dismissed after the ships return to port after exercises.During the training exercise five alien spacecraft arrive in response to the NASA signal. Their communications ship crashes in Hong Kong after hitting an Earth orbit satellite, while four others land in the water near Hawaii. Sampson, John Paul Jones, and the JMSDF Kongo class destroyer Myoko investigate, but are trapped when the alien mothership erects a tower that creates a force field over and around the Hawaiian Islands. The force field separates the 3 ships from the rest of the armada led by Shane.After shots are fired the aliens destroy Sampson and Myoko, and damage John Paul Jones, killing the commanding and executive officers. Alex takes command as the most senior officer left on the ship, while also learning that Stone was killed on the Sampson. The John Paul Jones recovers survivors from Myoko, including Captain Nagata, whom Alex is in a rivalry with.Meanwhile the aliens have taken over the communications array on O'Ahu. Nearby, Samantha, a physiotherapist, is accompanying retired Army veteran and double amputee Mick Canales on a hike to help him adapt to his prosthetic legs. They meet scientist Cal Zapata, who is fleeing from the array. Zapata informs them that the aliens are likely planning to bounce a signal to their home planet off NASA's Project Beacon satellite, but the satellite will not be in range for another five hours. Zapata then agrees to retrieve a radio that will allow Samantha and Mick to contact the John Paul Jones and relay this information.The crew of the surviving ship finds an alien floating in the water and bring him on board. Alex takes off the alien's helmet which causes the alien to gain consciousness & it does a kind of a mind meld with Alex & shows Alex that Aliens plan to bring an entire invasion force to the planet.Back on the John Paul Jones, the crew faces difficulty because the alien force field has disabled radar functions. Nagata suggests using the tsunami warning buoys around Hawaii to track the aliens, and as their ship monitors the NOAA buoy technology the surge of the advancing alien ships generates detectable wave action. During a night battle, the aliens and the humans exchange shots in a manner reminiscent of the "Battleship" board game. The John Paul Jones sinks two alien ships but is unable to hit the third. Alex had learned from crew mate Jimmy Ord that the aliens were sensitive to sunlight after they had captured one and decides to lure the third alien vessel close to shore, where he and Nagata shoot out its bridge windows as the sunrise blinds the aliens. In the ensuing battle, both ships are destroyed.Fearing the aliens are contacting a larger invasion fleet, Alex needs to destroy the alien mothership and tower next. But since his ship has been destroyed, the survivors are forced to return to base and acquire the only remaining naval vessel, the USS Missouri. Although decommissioned and turned into a museum ship, they are able to reactivate it with the aid of the retired veterans preserving her. The battleship manages to evade the alien weapons fire by deceiving the alien threat-detection system, engages the alien mothership with its powerful main guns and destroys the force field it was maintaining. Alex uses the last shell to destroy the communications array on the island, leaving the Missouri defenseless. However, with the force field barrier down, US Navy and Royal Australian Air Force jet fighters from the RIMPAC fleet arrive and eliminate the last alien vessel.A ceremony is held to honor the navy personnel and Alex asks Admiral Shane for his daughter's hand in marriage. The Admiral initially refuses but invites Alex to lunch to discuss the matter. A post-credits scene in Scotland shows three schoolchildren and a handyman running off in terror as an alien hand reaches out of an object they have just broken open.