The first step of Horizontal Directional Drilling (HDD) is the pilot bore. The hollow drill rods are pushed hydraulically through the ground. The drill head cuts a bore hole into the ground. Drilling fluid (Bentonite) is pumped through jet nozzles in the drill head to loosen the ground. The drill head has an asymmetric steering plate. As long as the drill head is rotated continuously, it cuts a straight bore hole. A sonde inside of the drill head transmits signals to the top and allows continuous locating of the drill head. To change direction, the rotation of the drill head is stopped in a position so that the steering plate points in the required direction. Now the drill head is pushed through the ground without rotation. Thereby it steers into the position (roll angle) of the steering plate.