The risk of gunfire is rising by the day. The year ended in March saw a record number of Japanese fighter jets scrambled against Chinese aircraft. In total, Tokyo deployed jets 810 times, up from 567 the previous year. All it takes is one midair collision. The same goes for the fast-increasing number of ships navigating disputed waters. A single mishap, overreaction or misperception would change the geopolitical calculus at Obama's Pentagon.