Last of the six axles Once the passenger fleets of America were ruled by C-C and A1A type units. No more, along with the their ill fated SDP40F bretheren, these were the last purpose built 6 axle passenger engines. While their HEP gave them much longer lifespans than the SDP40F's, the bulk of the fleet was replaced by new MP36's like the one to the right. The 611 and 614 were reactivated last year and are once again hauling passengers on their old Milwaukee stomping grounds, but no doubt they are on borrowed time.