During the American Civil War, the Yard once again became an integral part of the defense of Washington. Commandant Franklin Buchanan resigned his commission to join the Confederacy, leaving the Yard to Commander John A. Dahlgren. President Abraham Lincoln, who held Dahlgren in the highest esteem, was a frequent visitor. The famous ironclad USS "Monitor" was repaired at the Yard after her historic battle with the CSS "Virginia". The Lincoln assassination conspirators were brought to the Yard following their capture. The body of John Wilkes Booth was examined and identified on the monitor USS "Montauk", moored at the Yard.