The apparatus, provided for undersea work, includes a barrel holder, a barrel for guiding a fastener intended to be driven by the gases of a propulsive charge and a percussion system for setting off the charge. The percussion system includes a striker, a bolt for cocking the striker, a tumbler for releasing the bolt, a trigger for actuating the tumbler and a chamber having a liquid intake orifice and a suction orifice. The tumbler is movable in the chamber and the trigger, when operated, closes the intake orifice, pushes back the liquid and moves the tumbler thus allowing percussion of the charge. Upon return of the trigger into the rest and rearming position, the suction orifice makes possible to compensate the leaks in the chamber and to use the apparatus again.