I do hope that underneath these exotic beacons this had a Perkins 6-354 diesel engine, not the awful Jaguar 4.2 liter petrol one - which was very troublesome...
The Jag engine made these little D series Dennis water tenders a bit faster of course, but this was only when they were on the run!
Because Dennis did not build their own engines, they had to do their best with a very limited choice of vendors. If a brigade still wanted petrol, and quite a few did in 1968, it was either the B60 (as in the F8) or the Jag - and the Jag was lighter, smaller and a lot less expensive.
It also found its way into a distinctly odd prototype front wheel drive Dennis ambulance, which understandably never went into production.
But it was of course the beating heart of the E type Jag, which gave it a lot of emotional appeal!
I had the misfortune to be in charge of a factory in Belgium, where we built small tracked armored personnel carriers for NATO armies in the 1970s.
These had the same engine, and the percentage of these units which were unfit for duty as a result of engine problems was consistently around one out of every four. I can only imagine that the petrol D series suffered the same downtime...
Added by Avonmouth on 29 May 2018.