Before it assumed its role as a maximum-security lock-up, this 1912 cellhouse was renovated by the Bureau of Prisons. Tool-proof bars replaced the flat, soft-steel barriers of the military prison, and gun galleries were built at either end of the two main cell blocks (B and C). Outside, six guard towers were constructed, barbed wire was strung, chainlink fences erected, and metal-detectors installed. As time passed, further work was clone on the cellhouse; in 1939-1940, D Block (also called the Segregation or Treatment Unit) was extensively remodeled, and electric doors were installed.
