"420 horses from Somerset" So read the legend on the
back of the cab I passed on the M4 recently.
(I was making a coach journey, of course!).
But this was no horse-box: the horses were not behind the driver but under the bonnet. It is a long time since vehicles were rated in horsepower, originally to enable comparison of a motor with its predecessor horse and carriage.

The British standard horse has a power rating of 746 watts – about ¾ that of a 1 bar electric fire and rather more than that of the electric motor in a big vacuum
cleaner. The early Ford Model T car was 20 horsepower.

Many years ago I was amused to read a licence for a motorcycle which claimed to be powered by ICE. If only! But that was an acronym for Internal Combustion Engine – using petrol as fuel.

There may still be some people who imagine that vehicles can be powered by molten ice (water, that is). No such luck! What is more plausible is use of hydrogen as fuel which burns to form water with release of motive energy.
But hydrogen only rarely occurs uncombined. There has to be an input of energy to liberate it from water. So there’s no net gain using that hydrogen. Rather there will be a net input of energy in setting up and operating the plant, transporting the hydrogen as compressed gas from producer to user. The advantage
postulated is the ability to use renewable energy such as hydroelectric or solar energy in some remote location to make a product which can be piped around much as oil now is. There’s a long way to go realise such a scheme.