Escape!
Despite the prison's island location, a few Civil War prisoners tried to escape-in the end, always unsuccessfully. Among them was Pvt. Charles Sawyer, a Union deserter who widened this narrow musketry "loophole" (opening to the right), supposedly by piling hot coals on the granite edges until they cracked. Sawyer managed to squeeze himself out through the opening on October 1863. Avoiding sentries, he swam into the channel, where he was caught when a passing schooner picked him up. Afterwards the opening was blocked with cement and an iron bar, both visible today.
Courtesy hmdb.org
