The engine had a unique characteristic whine or whistle. As an avid train spotter at Waverley station in edinburgh I loved hearing it, saw every one and was in the cab of two thanks to long suffering kind engine drivers.
There was a mini deltic too. I'm not sure it went beyond a testbed loco.
https://en.wikipedia.org/wiki/Napier_Sabre (1938).
Powered the absolute monster that was the Tempest (up to the Mk 2 - they did have reliability issues they never quite solved but 3000+HP out of an engine that weighs barely more than a tonne dry will do that)
https://en.wikipedia.org/wiki/Hawker_Tempest
Was happy to see the name re-used for our upcoming fighter.
We also called the Eurofighter the Typhoon and the (WW2) Typhoon (also a Sabre engine) was the predecessor of the Tempest - it started as a re-wing of the Typhoon but enough changes where made to give it a new name.
Just a devastating superprop in its day.
[0]https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio... [1]https://en.wikipedia.org/wiki/Napier_Nomad
The youtube channel "Greg's Airplanes and Automobiles" has a nice video about turbo compound engines.
Generally speaking at least, two stroke diesel engines weren't super efficient, but did offer great power output relative to their size.
I have dim memories of being held up over a bridge to watch steam trains pass, but by the time I was obsessively writing down numbers they were special trains like "Sir Nigel Gresley" and "the Flying Scotsman"
I left britain before the east coast electrification. I do still see my favourite type 8 Diesel shunter, the most ubiquitous kind in Britain, when I pass by.
If you want sheer power, It's a Deltic every time. That high pitched whine, it's unmistakable.
I used to hear it all the time, working in a nearby industrial site. I'd maybe just take five minutes to sit outside and drink my coffee, listening to that weird shimmering howl.
There are no good recordings of it on Youtube and I suspect like a lot of things you have to experience it for yourself.