Research was expanded to the drilling of crystalline rock. Advance rates of 40 inches per minute have been achieved at 16,000 psi, 10 gpm flow rate in a 30,000 psi compressive strength rock using the water alone as the drilling mechanism. The quality of the hole achieved as the jet drilled a variety of rock was found to vary and a hydromechanical drilling bit, combining high pressure water jets with roller cones, has been developed. A field drilling unit has been tested and modified to allow the drilling of holes to 3/sup 1///sub 2/ inch diameter using the hydromechanical drill. Preliminary work on the development of a cavitation test for rock is also included