The Navy Cross is the second highest decoration, awarded for extraordinary heroism while serving in the U.S. Navy, or US. Marine Corps or US Coast Guard when operating under the department of the Navy.  Three criteria for the award, are to be engaged in combat action against an enemy of the United States, engaged in combat military operations involving conflict with an opposing foreign force, and engaged in armed conflict combat while serving with friendly forces when the United States is not a hostile party.
The award was established in 1919, due to the United States entrance into World War I.  Prior to this, the Medal of Honor was the only award for valor to the United States Navy.