The Good Conduct Medal is one of the oldest military awards

Awards and decorations of the United States military

Awards and decorations of the United States Military are military decorations which recognize service and personal accomplishments while a member of the United States armed forces...

 of the United States military. The Navy Good Conduct Medal was first issued in 1869, followed by a Marine version in 1896. The Coast Guard Good Conduct Medal was issued in 1923 and the Army Good Conduct Medal in 1941. The Air Force was the last service to create a Good Conduct Medal in 1963. The USAF discontinued the Good Conduct Medal for a brief period from February 2006 to February 2009.
The Good Conduct Medal is awarded to any active-duty enlisted member of the United States military who completes three consecutive years of "honorable and faithful service".