Ship Island is the largest of four islands twelve miles off the Mississippi coast in the Gulf of Mexico. In July 1861, Confederate troops occupied the island and began to fortify it. Subsequently, the installation was deemed untenable and Confederate troops fired their installations and evacuated. Sailors of the U.S.S. Massachusetts, with whom the fort had been trading shots for some time, immediately occupied the island and it became an important base for Union operations along the Gulf coast for the remainder of the war. (By John Osborne)