Folder: S.F. Islands-Alcatraz-Prison Breaks-May, 1946.
Newscopy (1946 May 3): "MASTER SWITCH--After overpowering a guard, revolting Alcatraz convicts threw a master switch controlling all cells in a block, similar to the control box (arrow) for Block D."
On back: "...It shows the entire control corridor generally referred to as 'D' block. As you will notice, the photograph was taken from the end of the corridor near the door where you enter, and the view is down the corridor from west to east showing the cells on first and second and portion of the third tier. It also shows the control box open indicating station from which officer may operate the devices for opening and closing cells. Next to the control box are the shower rooms of which there are two on each tier."