Commander of the nations armed forces?
President Kennedy orders the U.S. Navy to "quarentine" the island of cuba. Commander-in-chief acts as supreme commander of the nation's armed forces
The Commander in Chief of the US Armed Forces is the President of the United States - so his duties are the same as the President. The reason that the President is Commander-in-Chief is because in a democracy the armed forces must be controlled by elected civilians, rather than the other way around.