Abstract: A reverse circulation down-the-hole hammer drill apparatus for drilling rock and overburden comprises a fluid-driven piston which reciprocates in an annular chamber to repeatedly strike a bit suspended at one end of the chamber, for example in a splined mounting. Fluid is exhausted through the bit directly to the face of the bit and cuttings and debris are returned via a central throughbore in the bit and in the drill apparatus to the surface. The bit drops forward on encountering a void during drilling operations to open by-pass passages which exhaust fluid directly into the throughbore temporarily so as to prevent any loss of return of sample to the surface.