Built in 1943, by the Brunswick Marine Construction Company of Brunswick, Georgia (hull #102) as the Port Clinton for the United States Maritime Commission.
In 1945, the tug was acquired by the Dalzell Towing and Transportation Company (New Haven Transport Company) of New York, New York. Where she was renamed as the Captain.
In 1950, the Dalzell Towing and Transportation Company renamed the tug as the Fred B. Dalzell.
In 1964, she was acquired by the Portsmouth Navigation Company of Portsmouth, New Hampshire. Where she as renamed as the New Castle.
In 1964, the Portsmouth Navigation Company was acquired by the Moran Towing Corporation of New York, New York. Where the tug retained her name.
In 1982, the tug was acquired by Winslow Marine Incorporated of Southport, Maine. Where she was renamed as the Eliot Winslow.
In 2014, she was acquired by the Eastport Port Authority of Eastport, Maine. Where the tug was renamed as the Capt. Mac.
She is a single screw tug, rated at 2,500 horsepower.