By Jung Sung-ki Staff Reporter South Korea and the United States began their annual large-scale military exercise Sunday. The Key Resolve/Foal Eagle exercises involve about 27,000 U.S. troops, including 12,000 U.S. troops stationed on the Korean Peninsula and 6,000 from off-peninsula, according to a defense ministry official. Joint drills will be conducted through March 7 in multiple locations throughout South Korea, he said. The Key Resolve exercise, formerly known as RSOI (Reception, Staging, Onward Movement and Integration), is a simulation-driven, defense-oriented combined command-post exercise intended to evaluate the allied forces' capability to receive forces from bases outside the country in the case of an emergency on the peninsula. Foal Eagle is a theater-wide combined field exercise. It involves massive joint field exercises including rear area security and stability operations, special operations, ground maneuvers, amphibious operations and combat air operations. South Korean and U.S. troops have conducted the two war games simultaneously since 2002. The Sand Diego-based U.S. nuclear-powered aircraft carrier Nimitz and its striker group arrived in South Korea last week to participate in the drills. The 97,000-ton Nimitz pulled into Busan on Thursday, along with the San Diego-based cruiser Princeton and destroyer John Paul Jones. The destroyer Higgins, also from San Diego, is in Pohang, and the Hawaii-based Chaffee is in the East Sea. USS Ohio, the U.S. Navy's newly converted guided-missile submarine, is also participating in the war games. Commissioned in 1981, the Ohio-class submarine was originally designed for extended deterrence patrols and has a cruising speed of 12 knots surfaced and 24 knots submerged. North Korea routinely condemns the joint drills, which South Korea and the United States say are purely defensive, calling them a rehearsal for a pre-emptive strike against the regime. The two Koreas remain technically at war since the 1950-53 Korean war ended in a truce, not a permanent peace treaty. About 28,000 U.S. troops are stationed in South Korea as a deterrent against the North, which conducted its first-ever nuclear device test in 2006. gallantjung@koreatimes.co.kr