A drill head of directional boring includes a bit, a holder for a device for detecting angular orientation of the bit, and a hammer including a striker, wherein the bit assembly, holder and hammer are connected head to tail with the bit at a front end. The bit has a frontwardly facing main cutting surface having a plurality of main cutting teeth disposed thereon and a gage tower extending radially outwardly from the main cutting surface, which gage tower has at least one frontwardly facing gage cutting tooth thereon suitable for cutting over an angle defined by less than a full rotation of the bit. In one embodiment, the main cutting surface is substantially flat and circular and has fluid ejection ports thereon, and the drill head has passages for conducting a drill fluid therethrough to the ejection ports.