Research was conducted to develop, demonstrate, and deliver a field test model of a probe drill guidance system. This system was to be applicable to a transportable drill built for the Bureau of Mines to locate and aid trapped miners through a 28-inch-diameter hole from the surface. The drill guidance system was required to be operable to a depth of 2,500 feet and to enable the probe drill to hit a 5- foot-diameter target at a depth of 1,500 feet. A unique cableless system was developed that employed the drill pipe as one conductor and the earth as the other conductor, constituting a complete electrical circuit. The field test model proved every aspect of system performance but was unreliable as an operationally ready system.