Washington, D.C. ? On the night a torpedo-armed North Korean submarine allegedly sank a South Korean patrol ship, the U.S. and South Korea were engaged in joint anti-submarine warfare exercises just 75 miles away, military officials told The Associated Press.

The sinking of the Cheonan was the worst South Korean military disaster since the 1950-53 Korean War. It showed that even impoverished nations such as North Korea can inflict heavy casualties on far better equipped and trained forces, including those backed by U.S. military might.

Defense Secretary Robert Gates said plans for more joint U.S.-South Korea anti-submarine exercises, announced after Cheonan went down, are on hold awaiting U.N. action on the incident.

That’s in part, Gates said Friday while in Asia, because of concerns about instigating another rash act by the North Koreans.