The Gas Turbine compressor needs to be turning all the time, and driving this via the CT turbine takes most of the fuel, whether no load or full load. Therefore the machine is only really efficient flat out.
Jet engines are simply gas generators, with no power turbine coupled to a power output, eg gearbox and driven unit, such as a generator.
Railway duty cycles mean that GTs are unsuitable for rail applications.
The Union Pacific GTs would have performed well working at high speed/full load, and UP invested heavily in them, but advances in diesel technology saw them superseded.
But for WW2, the UK may have seen a fleet of LMS Turbomotives working the West Coast expresses.