Perhaps it goes without saying that this was very expensive, and the U.S. military was very interested in a cheaper alternative, and so looked to nuclear reactors. When the central control rod was disconnected, a C-clamp was attached at the level of the floor above the reactor to support the weight of the control rod while the control rod drive mechanism was disconnected. To enable the control rod to be lifted, a handle was attached in the place of the control rod drive mechanism. The procedure called for the control rod to be lifted no more than 2 inches to disconnect the clamp. Subsequent investigation has shown that the control rod was lifted 20 inches or more out of the core.