which are well known and are not shown since they are not material to this invention penetrator 10 is provided with four hinged terra fins 12 13 14 and 15 preferably located at the nose or forward end of the missile and hence are called 34 canard 34 type terra fins it should be understood however that these fins may be located at either end or in the middle section of the missile the fins are hinged from the aft end prior to impact the fins are symmetrically disposed in orthogonal planes as shown in fig1 b upon impact the forward edge of any fin subjected to off axis impact forces will swing downward in inertial reaction to the impact of the penetrator with the ground surface media 16 as shown in fig1 c and d in other words the hinged terra fins induce a negative angle of attack on the penetrator upon impact with the surface media thus instead of penetrating along the line 18 of fig1 a or being rotated upward as the penetrator tries to follow the path of least resistance the penetrator is caused to rotate as shown in fig1 e to an equilibrium angle of attack along the line 20 thereby executing a 34 downward tuck 34 maneuver the details of the hinged terra fin construction are depicted in fig2 4 the penetrator 10 has an external cylindrical body 19 which tapers to a nose cone 24 at the forward portion four hinged terra fins 12 13 14 and 15 are pivotally mounted on the penetrator body so that when the penetrator is subjected to lateral impact loads the fins will rotate to a.