The paper reviews past research on pulsed high-pressure water jets and their application to breaking rock. Experiments are reported showing the input energy per unit volume required to fracture various types of rock as a function of the pertinent variables. The stagnation pressure of the liquid jets was varied from 50,000 to 5 million psi. The theories of jet penetration through water and rock are compared with experimental results. The feasibility and potential advantages of using pulsed water jet equipment for ocean-floor excavation are discussed.