1. IN A ROCK DRILLING APPARATUS, THE COMBINATION OF: (A) A PERCUSSION TYPE DRILLING TOOL COMPRISING, A ROTATING SHAFT, AND A ROTATIONAL CONTROL MECHANISM FOR REGULATING THE DIRECTION OF ROTATION OF SAID SHAFT; (B) A SOURCE OF FLUID UNDER PRESSURE; (C) A PRESSURE FLUID SUPPLY LINE CONNECTING SAID SOURCE OF PRESSURE FLUID TO SAID PERCUSSION TOOL; (D) A REGULATING VALVE IN SAID PRESSURE FLUID SUPPLY LINE FOR REGULATING THE AMOUNT OF PRESSURE FLUID DELIVERED TO SAID PERCUSSION TOOL; (E) REMOTE VALVE MEANS CONNECTED AT ITS UPSTREAM SIDE TO THE PRESSURE FLUID SUPPLY LINE UPSTREAM OF SAID REGULATING VALVE AND AT ITS DOWNSTREAM SIDE TO THE ROTATIONAL CONTROL MECHANISM, TO CONTROL THE FLOW OF FLUID TO SAID MECHANISM TO OPERATE SAID MECHANISM; AND (F) INTERLOCK MEANS CONNECTED TO THE PRESSURE FLUID SUPPLY LINE DOWNSTREAM OF THE REGULATING VALVE AND DISPOSED TO COACT WITH SAID REMOTE VALVE MEANS TO PREVENT SAID REMOTE VALVE MEANS FROM SUPPLYING FLUID TO THE ROTATIONAL CONTROL MECHANISM FOR OPERATING SAID MECHANISM SO AS TO PREVENT SAID MECHANISM FROM REVERSING THE DIRECTION OF ROTATION OF THE SHAFT WHILE FLUID IS CONTINUOUSLY FLOWING THROUGH THE REGULATING VALVE.