High Quality Content by WIKIPEDIA articles! USCGC Mackinaw (WLBB-30) is a 240-foot (73 m) vessel built as a heavy icebreaker for operations on the North American Great Lakes for the United States Coast Guard. IMO number: 9271054. She should not be confused with a namesake ship, the USCGC Mackinaw (WAGB-83), IMO number: IMO 6119534, which was decommissioned on June 10, 2006.