U.S. and South Korean naval ships fired artillery and dropped anti-submarine bombs off South Korea's east coast Tuesday, the third day of high-profile military maneuvers intended to warn North Korea against any aggression. The dramatic show of force comes four months after a South Korean warship sank in the waters off the Koreas' west coast, killing 46 sailors. An international team of investigators determined that a North Korean submarine fired a torpedo that sank the ship in what Seoul called the worst military attack on it since the 1950-53 Korean War. The Korean peninsula technically remains in a state of war because the conflict ended in a truce, not a peace treaty. On Tuesday, both Koreas and the U.S. marked the 57th anniversary of the signing of the armistice against the backdrop of the military drills. "Since our nation's founding, the United States has relied on our armed forces to ensure our safety and security at home, and to protect lives and liberties around the globe," President Barack Obama said in a statement marking the anniversary. "I call upon all Americans to observe this day with appropriate ceremonies and activities that honor our distinguished Korean War veterans."