The gentleman who suggested E. Pass for the 'E.P &Co' marked 80w charging sets has now sent me a copy of his source material and very interesting it is too. Title of the paper is as subject of this post, written by K. H. Tuson M.I.Mech.E., M.I.E.E., F.Inst.P. and read before the Installations Section (of what I don't know) on the 17th of April 1947.
Not that much about the 80w set, save to say that it was developed by the Directorate of Scientific Research in 1942 as a result of experience in Norway and production (by Pass) started in 1943.
It is particularly revealing about sets for the 40mm Bofors gun though. Apparently power control for this gun had been developed by Sept 1939 but little thought had been given to its power supply. The set was originally intended to be mobile and size so weight limits were specified and tenders were obtained in Jan 1940. Initially three types were chosen powered by a four cylinder water cooled four-stroke "in great demand for fire pumps", a single cylinder air cooled two-stoke and a flat twin air cooled two stroke. None of the sets met the size and weight requirements but despite being the largest and heaviest the four-stoke set was by far the most satisfactory (the portability was found to be unnecessary anyway) and production of the two-stroke sets was eventually stopped. Why? Various reasons are given but - "Perhaps the biggest trouble was that troops were not accustomed to petroil lubrication and, in spite of warning notices, persistently failed to add oil to the petrol" - so don't be surprised if your Scott PAB or Enfield flat twin is totally knackered!
Various other sets are also described, including one for a mobile early warning radar, an example of which was "mounted on the Great Pyramid of Cheops during Mr Churchill's conference with President Roosevelt near Cairo in 1943". This appears to be driven by a Douglas FT?? (the one that resembles a Dragonfly motorcycle engine). Also Comment is made on the Norman flat twin as "a most excellent design which gave very good service, but was complicated to manufacture and slow in production".
In my view these sets are a bit of an overlooked area of preservation - the military enthusiasts' tend to concentrate on vehicles, weapons and uniforms, while most engine collectors find military gen sets rather drab and uninteresting. Display a nice Scott PAB howling away next to a 40mm Bofors gun and at least you wouldn't have to field the 'yes but what did it do?' question as it automatically traversed to take out a Jumbo coming out of Heathrow!