I would have to say 2 loco's, the class 43 (HST 125). Built from 1975 to 1982. Hold the
Official Record for fastest diesel, and only a total of 4 have been scrapped. They were only built as a temporary loco, while the ATP was developed, but because the APT was a failure, they have stuck. The Australian XPT is HST derived.
The HST:
Another successful locomotive is the Class 55 Deltic, built from 1961 to 1962, withdrawn in 1982, there are 6 in preservation, and 1 is still in mainline freight use, by GBRf. It uses Napier-Deltic
Naval engines. The 1 in use for freight is hauling EMU's for refurbishment, and it has to go the long way round, because it would set off tunnel smoke alarms.
The Class 55 Deltic.
