During the war, Alco put together a portable steam-powered generating set designed to be parachute-dropped behind the lines allowing forces on the ground to recharge their radio batteries. Comprising a portable boiler connected to the 1930's-designed Stuart Turner Sirius engine, many were made and, reputedly, deployed. They're somewhat scarce now, although I did have one in last year.
Following on from the success of the little "Firefly" set, a larger, purpose-designed unit was built. Stuart Turner supplied a single cylinder, piston valve engine with the generator end-plates cast in to the crankcase. This sat in a cradle coupled to the 6 volt generator and included a variable stroke boiler feed pump.
The boiler came in three parts: grate, firebox and horizontal cast-aluminium barrel. The chimney was again in parts, collapsing for transit. The boiler is coupled to the engine with flexible pipes for steam and exhaust, there is another pipe terminating in a perforated rose designed to be thrown into the nearest stream for feed water. Working pressure is 60 psi, the boiler is designed to be fired on anything that came to hand - it goes well on wood. There is a very heavy-duty water gauge which looks designed to be squaddie-proof.
This unit is substantially complete - a couple of the rubber hoses have been replaced over the years and there is no regulator valve (which was a simple wheel valve). It fits into the wooden crate rather neatly, although the original box was a huge great thing designed to be parachute dropped and weighing about a ton.
I believe that 400 of these units were made, with 200 disposed of by the military on the surplus market after the war - the rest are probably still in strategic reserve and will be issued to key personnel in the next one. Very rare nowadays, I have only ever seen one other which came in last year. In the spirit of enquiry we're renowned for here, I steamed that one up to see how it went - amazingly, for such a barmy looking contraption, they go very well and actually do the job intended!