A small 3 Mega-Watt reactor developed by the US Army for supplying power to forward deployed troops. Went prompt critical when a technician manually removed a control rod to insert a flux measuring device to monitor the core. Reactor power spiked to 300,000% and the water in the core was flashed to superheated steam. Since steam is less dense than water, the control rod was ejected from the core, pinning the technician to the ceiling of the building. Radiation alarms sounded in a fire house 5 mi away.