1. Direct impact of the striker mass on the rock can greatly increase the impact energy and the efficiency of the apparatus. 2. Automatic operation of the mechanism for opening the ports increases the frequency of impacts of the hydraulic drill. 3. A hazardous state which can occur in the absence of obstacles to impact can be avoided by appropriate design of the composite piston so as to brake the impact mass without expansion of the pneumatic spring. 4. In contrast with drilling and blasting, rock breaking by means of a high-energy hydraulic drill does not disturb the stratified structure of the rock and thus much reduces the possibility of rock falls and flooding of the working—this is especially important when cutting underwater tunnels and subways. 5. Our studies with high-energy hydraulic drills suggest that rock breaking with high impact energy may in the near future become the main method of making working in rocky ground, owing to its cheapness, universality, and capability of organization as a continuous process.