South Korean and U.S. troops began five days of naval drills on Monday, AP reported. The drills involve fighter jets, helicopters and 40 naval ships and submarines from the allies, including the aircraft carrier USS Ronald Reagan, according to South Korea's navy. Spokesman Jang Wook told reporters the drills are aimed at practicing how to respond to a potential naval provocation by North Korea and improving the allies' combined operational capability. The drills were to include live-fire exercises by naval ships and aircraft and anti-submarine training.