Provided is apparatus for use in resonance enhanced rotary drilling, which apparatus comprises: (i) an upper load-cell for measuring static and dynamic axial loading; (ii) a vibration isolation unit; (iii) optionally an oscillator back mass; (iv) an oscillator for applying axial oscillatory loading to the rotary drill-bit; (v) a vibration transmission unit; (vi) a lower load-cell for measuring static and dynamic axial loading; (vii) a drill-bit connector; and (viii) a drill-bit, wherein the upper load-cell is positioned above the vibration isolation unit and the lower load-cell is positioned between the vibration transmission unit and the drill-bit, and wherein the upper and lower load-cells are connected to a controller in order to provide down-hole closed loop real time control of the oscillator. Further provided is an apparatus for use in resonance enhanced rotary drilling, which apparatus comprises: (i) an upper load-cell for measuring static loading; (ii) a vibration isolation unit; (iii) an oscillator for applying axial oscillatory loading to the rotary drill-bit; (iv) a lower load-cell for measuring dynamic axial loading; (v) a drill-bit connector; and (vi) a drill-bit, wherein the upper load-cell positioned above the vibration isolation unit and the lower load-cell is positioned between the oscillator and the drill-bit wherein the upper and lower load-cells are connected to a controller in order to provide down-hole closed loop real time control of the oscillator.