In the summer of 1987, the Santa Fe Cleburne Shops, located in Cleburne, Texas took ATSF U23B #6332, and began the prototype program. ATSF #6332 was chosen for it suffered wreck damage, and thus became the right locomotive at the right time for this particular rebuilt program.

      In July 1987, the Cleburne Shops released the prototype for evaluation on the feasibility of a rebuilding program for Santa Fe's remaining U23B locomotives. The ATSF #6332 was professionally transformed into a new class, the SF30B [Santa Fe (SF), 3000 HP (30), B-B trucks (B)], and renumbered #7200.

      The new SF30B prototype had numerous physical, cosmetic, and internal changes from its humble beginnings as a U23B unit. For starters the locomotive's horsepower was increased from 2300 to 3000 hp, as the Cleburne Shops installed a General Electric 7FDL-12F30UX prime mover. The electric systems were modified to Dash 7 standards, and Sentry Wheel Slip capability was added. The original 3,250-gallon fuel tank was maintained, however overall capacity was reduced to 2,900 gallons, as a section was used as a retention compartment/tank. The fuel tank was also expanded into the frame, giving the 45 degree black angle into the side sill. The fuel filler was also moved higher onto the side sill, however by November 1989, the fuel filler was moved back to its former lower position. The crew cab dimensions remained the same, however was moved forwarded in order to house a new electrical control cabinet. The cab also received a Cleburne-manufactured nose - similar to the one constructed for the SF30C. The new SF30B also lost its original front and rear drop steps - in favor of anti-climber pilots.

      In the engine area, the oil-bath air filters were replaced with paper filters, and the radiator section was completely Cleburne-fabricated, giving the locomotive a very unique end profile - complete with crew ladder instead of grab irons. The radiator area, although completely reconstructed still held the same amount of cooling water - 350 gallons. The roof was also unique as the new primer mover contained a new, oversized exhaust stack, which can also be found on the Dash 7 model. Operating in the arid desert, Santa Fe also added a cab air conditioning unit, as well as repositioned the horn. To lessen the wear of the wheels on rail curves, a flange lubricator tank was also added behind the cab on the conductor's side.

      Originally, the SF30B rode on AAR type "B" trucks, however by 1993, the floating bolster trucks from the retained B39-8, #7401, were utilized, and by 1996 the SF30B was outfitted with ditch lights.

      Overall the prototype SF30B was deemed a success, however by this time, the age of contracting locomotive maintenance outside of a company had become a way of life, and the Cleburne Shops were closed, leaving #7200 as the only one of her kind. General Electric was contracted to maintain Santa Fe's GE-built locomotives, and this included the SF30B, although the rest of Santa Fe's U23B fleet had been purged from the roster. In order to maintain a general maintenance schedule, the SF30B was renumbered into Santa Fe's fleet of B23-7 locomotives, and given a new number, #6419. General Electric also derated the horsepower of #6419 from 3,000 back to 2,300 horsepower, as GE did not wan to be responsible for the possible stress caused by the former high rating.

      The SF30B made it through another purge during the combination of diesel fleets when Santa Fe merged with Burlington Northern to form the expansive BNSF Railway. The new company renumbered the unique locomotive once more, and today wears #4276, and can be found in regular BNSF manifest freight, and local, service.