A state-of-the-art icebreaker when she was launched in 1944, Mackinaw was built to extend the shipping season on the Great Lakes into the winter months and thereby strengthen the wartime economy of the United States during World War II.

Unlike the U.S. Coast Guard's large icebreakers before and since, Mackinaw was designed specifically for use in the shallow, freshwater Great Lakes.

[6] Another influence was Lieutenant Commander Edward Thiele, USCG, who travelled to Europe on vacation just before the United States entered the war and informed himself of modern icebreaker designs, particularly that of the state-of-the-art Swedish Ymer.

[7] Finally, the icebreaking features of Great Lakes rail ferries which operated in heavy ice in the Straits of Mackinac were studied.

[17][18] However, Mackinaw's design shares many characteristics with that of the Wind-class icebreakers, such as a relatively short length in proportion to the great engine power developed, a cut-away forefoot, rounded bottom, and fore, aft and side heeling tanks.

[26][27] For ground tackle Mackinaw shipped two 6,000 lb (2,700 kg) stockless bower anchors, each with 90 fathoms (160 m) of chain composed of 2-inch-diameter (51 mm) links.

The Mackinaw was then the largest member of a collection of icebreaking Coast Guard cutters on the Great Lakes which also included 180-foot buoy tenders[33] and 110-foot tugboats.

[36][Note 1] The Mackinaw and these other Coast Guard icebreakers provided safe passage for freighters as they delivered their cargo of taconite, grain, and other resources around the Great Lakes to ports such as Detroit, Chicago, and Gary.

Mackinaw's icebreaking season each year depended on that winter's ice accumulation on the Great Lakes but typically lasted about 70 days.

Mackinaw returned the next spring with the USCGC Acacia and during March 17 and 18 broke a passage into the ice-locked harbor which allowed 12 ships to leave.

[39] [40] [41] Mackinaw returned to Buffalo again in April 1961 to lead Tupelo and the Coast Guard tugboats USCGC Kaw and Ojibwa in escorting vessels in and out of the ice-clogged harbor.

[42] The Mackinaw did not routinely perform search and rescue missions; these were normally carried out by smaller, faster, nimbler Coast Guard cutters, boats and aircraft.

[43] The Mackinaw's first large search and rescue mission was not until the disappearance of Northwest Orient Airlines Flight 2501 over Lake Michigan on the night of 23 June 1950.

Mackinaw, along with other Coast Guard and Navy ships and state police forces, fruitlessly searched for survivors and instead collected airplane debris and human body parts from a wide swath of Lake Michigan.

[48] On the afternoon of November 29, 1960, the freighter SS Francisco Morazan ran aground in a snowstorm off South Manitou Island in Lake Michigan.

[50][51] On May 10, 1965 Mackinaw was on-scene commander of the Coast Guard's rescue efforts after the Norwegian ship MV Topdalsfjord collided with and sank the U.S. bulk carrier SS Cedarville near the Mackinac Bridge.

[53] On November 19, 1966 the German freighter MV Nordmeer grounded and sank in shallow water seven miles north of Thunder Bay Island in Lake Huron.

[54] The salvage crew radioed for help on November 29 and the Mackinaw returned to the vicinity, but the weather and the Nordmeer's position on Thunder Bay Shoal made it impossible for the icebreaker to approach the stricken freighter.

[57] Early on December 8, 1976, the ore carrier Cliffs Victory was forced out of her channel on the Saint Marys River by a sudden surge of current-driven ice and ran aground.

After some of the Cliffs Victory's cargo was unloaded into a barge, the Mackinaw tried unsuccessfully all the next day to pull the ore carrier off the submerged shoal on which she was grounded.

In the meantime, more than 60 other ships had lined up waiting for the river to be cleared, including six ocean-going freighters hurrying to reach the St. Lawrence Seaway before it closed on the 18th.

The closing chapter of the icebreaker's service history finally opened in December of 2000, when the Coast Guard called for designs of the ship's replacement.

The annual cost of maintaining the ship was a little over US$4 million, and Coast Guard spokesman Jack O'Dell said at that time, "She's extremely old, and she's just becoming impossible to operate.

In the spring of 2004, the Cheboygan City Council sent out feelers to its constituents to see if any group would be willing to take possession of Mackinaw after its projected decommissioning in June 2006 and to keep the ship in the Mackinac Straits area—ideally in Cheybogan.

Michigan's congressional delegation was enlisted to help and introduced legislation which directed the Coast Guard to convey Mackinaw to Cheboygan upon decommissioning.

The IMMM began work on a backup plan to host the museum in Mackinaw City, a village 15 miles north of Cheboygan.

[72] Mackinaw City's high tourist traffic would improve the museum's financial viability, and a member of the IMMM's board owned suitable moorings there at the former railroad dock for the ferry SS Chief Wawatam.

[75] The Icebreaker Mackinaw Maritime Museum is moored at the eastern end of the old SS Chief Wawatam railroad dock; entry to the area is just south of Shepler's Marine Service.

Visitors can tour the mess deck, the captain's quarters, bridge, engine room, wardroom, sick bay and other areas.

[76] The Charlevoix, Cheboygan, Emmet Counties Public Service Communications Organization (CCECPSCO), has established a full-time amateur radio station on board the Icebreaker Mackinaw Maritime Museum.