As a personal tribute to a legendary achievement exactly 75 years ago, I thought it appropriate to indulge in this little demonstration. Using the footage I captured a couple of weeks ago and adjusting replay speed over a measured 1 mile to 28.6 seconds, we can re-create the image of 60009 Union of South Africa running at an apparent 126 m.p.h. As a comparison I have included images of simulated 75 and 90 m.p.h. to demonstrate just how impressive a speed of 125.88 m.p.h. (to be exact) is for a steam locomotive. The removed streamlining of the B.R. form of A4 shows the motion fully exposed and demonstrates that the limiting factors for speed on a conventional steam locomotive are not just that of overcoming drag but (and maybe more importantly) the survival of motion bearings trying to cope with the extreme out-of-balance forces at such high rotational accelerations. In fact, aniseed was mixed in with the bearing lubricating oil on Mallards record run of 3rd July 1938 in order to produce a "nasal" warning if bearings overheated! 126 m.p.h. may not seem to be particularly high in terms of "record" speeds on today's railway but remember that this record was set way back in 1938 and hopefully after viewing this clip you, like me, will appreciate a little more just how exceptional that achievement was.