 The final three were converted from RB-57A aircraft and delivered in March 1967.The converted RB-57As differed from earlier "First Chip" conversions by the addition of a Mk III Impact Probe in the bomb bay.In March 1968 the 63-13286 prototype was also upgraded to the "First Chip" standard and the two phases renamed in accordance with newly established "Big Safari" nomenclature that required two-word code names beginning with "Rivet."