Spend part of a shift in a busy tower. The Baltimore and Ohio Chicago Terminal 75th Street tower in Chicago in 1968 had no radio, no electronics and no dial phone It did have a mechanical interlocking machine that the operator used to handle over 50 trains a shift on the B&OCT, Pennsylvania, Belt Railway of Chicago and Norfolk and Westenrn [Wabash].
This Adobe Acrobat multimedia presentation on CD contains recordings made in the tower in 1968, an explanation of the audio and the traffic being handled, and photographs and diagrams.