A mobile tunnel boring unit , wherein the unit comprises: a support body driven by first drive means , the first drive means for driving the mobile tunnel boring unit including a pair of spaced apart crawler tracks in contact with the tunnel floor and related track driving means to move the tracks , and thus the support body ; a cutter head drive means located at an operatively front end of the support body , to which is fitted a rotatable cutter head that has been pre-installed in a starting chamber , proximate a tunnel face to be bored, so as to rotatably drive the rotatable cutter head , in use; a muck hopper and a first conveyor arrangement , the cutter head comprising a full face cutter head fitted with cutters to bore a tunnel face , the cutter head being arranged to allow cuttings to pass through the cutter head for discharge into the muck hopper and onto the first conveyor arrangement , the cutter head drive means and a rear portion of the cutter head defining aligned central apertures through which a front part of the first conveyor arrangement can extend; a telescopic shield arrangement to shield the boring unit , the shield arrangement comprising a front shield proximate the front of the mobile tunnel boring unit , from which the cutter head protrudes and for accommodating the cutter head drive means , the front shield also having been pre-installed in the starting chamber together with the cutter head , and a rear shield that surrounds at least an upper portion of the mobile tunnel boring unit , the front and rear shields operating telescopically relative to each other, to accommodate changes in the boring direction; and an actuating arrangement comprising a plurality of hydraulic thrust cylinders extending between the cutter head drive means and a pair of opposite first gripper assemblies . a support body driven by first drive means , the first drive means for driving the mobile tunnel boring unit including a pair of spaced apart crawler tracks in contact with the tunnel floor and related track driving means to move the tracks , and thus the support body ; a cutter head drive means located at an operatively front end of the support body , to which is fitted a rotatable cutter head that has been pre-installed in a starting chamber , proximate a tunnel face to be bored, so as to rotatably drive the rotatable cutter head , in use; a muck hopper and a first conveyor arrangement , the cutter head comprising a full face cutter head fitted with cutters to bore a tunnel face , the cutter head being arranged to allow cuttings to pass through the cutter head for discharge into the muck hopper and onto the first conveyor arrangement , the cutter head drive means and a rear portion of the cutter head defining aligned central apertures through which a front part of the first conveyor arrangement can extend; a telescopic shield arrangement to shield the boring unit , the shield arrangement comprising a front shield proximate the front of the mobile tunnel boring unit , from which the cutter head protrudes and for accommodating the cutter head drive means , the front shield also having been pre-installed in the starting chamber together with the cutter head , and a rear shield that surrounds at least an upper portion of the mobile tunnel boring unit , the front and rear shields operating telescopically relative to each other, to accommodate changes in the boring direction; and an actuating arrangement comprising a plurality of hydraulic thrust cylinders extending between the cutter head drive means and a pair of opposite first gripper assemblies . <EOS>