LNER Mk3 TFO CoachHOR R4929C Hornby LNER, Mk3 Trailer First Open (TFO) , Coach M, 41115 Era 11 In order to allow running at 125 mph on Britains Victorian era railways, new rolling stock was needed by British Railways. Significant improvements over the Mk2 included new secondary air suspension between the bogies and the coach body as well as aerodynamic skirting on the underframe. Mk3 coaches are 75ft (23m) long enabling far greater capacity than older coaches. Mk3