Dear John (2010)

South Carolina US Army Special operations soldier John is on summer leave from his German base, visiting his widowed father. Being gallant on the pier, he befriends college student Savannah, a college student, and her buddies, a terminal father and his angelic son. John falls in love with Savannah, who diagnoses his beloved, gentle but weird father as mildly autistic. He plans not to sign up again, but 9/11 changes that, and she won't wait idly while their friends desperately need help.