I remember deltics well of course, even if i had a fleeting relationship to them in their BR service swansong when I was a nipper. Deltics weren't a locomotive you just saw and heard, you felt their power and prescence.
By the last old days of 1980 the deltic reign had ended. All be that ten years after the anticipated life time on the ECML metals. Just as with the pacific steam locos the deltics replaced, they themselves were superceded . They had become dinosaurs.
Or had they? In reality the fleet got a stay of execution in 1978 and ploughed on with various east coast and the final rather ill suited liverpool - newcastle semi fast diagrams. Rationalised with two of their brethren becoming parts bins, the rest in reality kept as an exhibition fleet into 1980.
The remarkable thing is that the remaining locos have survived much longer in preservation: now more than half as long again as their active service wijth BR. The "third age" of the deltics with proffessional management and main line certification.
What then for the alternative history where BR or a private body supported their utility say another decade in service?
Well if privatisation had been happening in the 1970s then gyou can bet that they would have been. A private railway would not have invested in a hundred 56s and the entire class 58. Standardisation versus reliability was a BR mantra , the opposite has been seen across europe and the usa. So the brush type 4 and its under delivered promise and poor reliability would have stopped the later builds. Class 50s would have been sent back to by then GEC leaving deltics, peaks and the more reliable hydraulics to be the main 100mph service providers outside HST diagrams.
Another alterntaive future would have been re-engining. By 1980 the Ruston Paxman Valenta would have been available in either a v8 at 1650bhp or a v16. Twin v 12s could maybe fit in a deltic, giving them thus standard units to hst and an RA 6 not to mention 4000 bhp plus!
Maybe other improvements to lub oil and piston / crank systems in the deltic power unit could have made them less smokey and extended service interval to over 3000 hours. Or a turbo version tuned for efficiency.
Whatever the locos when compared to ageing 45s and dodgey engined 47s , deltics were only a tad more smokey and it was burnt oil not spewing diesel and lub. They werent the only relics of the rush to dieselise which were environmentally non PC even by the mid eighties.
Where would they have worked?
If there had been a gap for them to work in an extended lifetime, then it would have been in the west country that they would have thrived. Well into the 1980s there were enough north to south west diagrams with loco change from WCmL or the need for speed from Newcastle or York right through.
However there were also 50 class d400s and seemingly endless ETH peaks in the post oil-sloshing GWR. Not to mention duffs a plenty, one fails send out another until you are down to 47/3s and ice cold trains!
Deltics had higher ETH capacity than 50s and arguably better performance in the 85 to 110 mph range. However it was only the eastern depots, Paxman colchester and donnie works who had the expertise needed in the early 80s in order to keep an ageing fleet going. Newcastle could then have been a centre for diagrams NE-SW with temporary stabling and driver training only at brum and bristol.
As a small, specialist fleet though there could be a case for remote allocation of servicing.
My own choice would be phasing out 50s over to HGR and including an upgrade to their eth. Thus allocating them to semi fast passengers, over night sleepers and speedlink on the ecml,. Then having 15 deltics allocated to Doncaster with a preserved demo fleet of four to newcstle and haymarket for railtours.
The donne main liners would actually work the west country with extensive drijver training for the wcml to Sw services during the day and the brum and newcastle sleepers at njight. This would be only to 1986 when boilered "bedz" were finally erradicated and enough hsts were released from ecml electrification to free up class 50 to take over any remaining GwR services in their new proven and fully rectified guise.