DRIVER WAS LEAVING BASE YARD WITH 2004 FORD F350 SD. WHILE DRIVING ON A SIDE STREET AT APPROXIMATELY 15 MPH, THERE WAS A TOTAL LOSS OF STEERING CONTROL THE VEHICLE CRASHED INTO A CHAIN LINK FENCE AS THE DRIVER WAS TRYING TO BRAKE TO A STOP. THE STEERING SECTOR SHAFT SHEARED OFF RIGHT AT THE PITMAN ARM.