On Fri, 18 Aug 2017 08:05:27 +0100, Richard Smith
wrote:

Not "clutch".
There were "diesel-hydraulic" locos in Britain.
"Hymek" and "Warship Class" (???).
Were they British "licences" of German designs?
Seems a very German example of precision engineering - not easily
replicated elsewhere.
Advantage is said to be that hydraulic-mechanical transmission weighed
less than electric transmission, so could pack more punch if the loco
had to be small and light due to track / axle-load, etc.
Check the real facts if interested.
Used primarily on narrow guage??