The Coast Guard Cutter Mackinaw, a 240-foot Icebreaker homeported in Cheboygan, Mich., breaks through ice that is 16-20 inches thick about five miles off the Duluth shoreline, March 16, 2013. The Mackinaw is the only U.S. heavy ice breaking resource assigned to the Great Lakes and in addition to heavy icebreaking other missions of the crew include servicing buoys, search and rescue, law enforcement, and the ability to deploy an oil skimming system to respond to oil spill situations.