The Great Isaac was a huge V-4 class seagoing tug and salvage vessel named after the 152-foot high lighthouse on Great Isaac Island near Grand Bahama.  The 185-foot tug was launched in 1944 from Boston, Massachusetts.  Although she was built to tow concrete oil barges, this task never materialized.  During wartime she had a platform-mounted, three-inch, anti-aircraft bow gun and two 50-caliber machine guns aft of the flying bridge, along with the Navy personnel to operate them. <P>The Great Isaac was towing the Liberty Ship Thomas M. Coolly from Norfolk, Virginia, to New York in dense fog when she was rammed by the Norwegian freighter Bandeirante.  The bow of the freighter plunged six feet into the Great Isaac's engine room, and she sank immediately.