A machine for boring tunnels comprises concentric outer and inner sleeves (2, 4) between the forward extents of which is defined an annular housing (6). A spiral auger (8) extends axially through the inner sleeve (4) and carries at its forward end a primary cutting head (10), while an annular secondary cutting head (14) is mounted in the annular housing (6) and is rotatable about the central axis of the sleeves (2, 4) on rotation of the auger (8). A series of steering plates (20) are spaced circumferentially about the forward extent of the outer sleeve (2) and are pivotal outwardly of said sleeve (2) on actuation of associated control members (22) to control the direction of movement of the machine on thrusting of said machine through the ground by an associated thrust mechanism reacting against the rear ends of the sleeves (2, 4) and providing power for rotating the auger (8) and associated cutting head (10,14).