I'm thinking it's a type of rocket, as the diagram shows a venturi, presumably each has more than one venturi? The copper tube with holes in it and the green coloured part of the diagram may be propellant and the means of initiating it, to launch the rocket from the steel tube, perhaps electrically, via the hole in the base end of the tube. The diagram shows a weak link between the copper tube and base of the `rocket', probably meaning that it is designed to break off at some point. I'm guessing that the blue colour in the diagram is propellant, to maintain or increase the flight speed; the yellow could be HE filling and the fuze appears to be a mid 20th century shape, assuming that it is British. Photo 3 shows what might be an obturating band, similar in principle to mortar ammo. Perhaps a number of the steel tubes containing rockets were designed to be loaded into a weapon for multiple firings. None of my copies of the 1874, 1902, 1915, 1926 and 1936 British ammo publications shows anything quite the same. For increased accuracy each rocket would need to spin in flight. Interesting and thanks for showing it.