In 1939, with a view to doubling production of aluminium articles intended for the war industries, and based on the adaptation of modern American processes for sheet metal production, the French Minister of Defense, Raoul Dautry, launched a project for the construction of a new factory for light alloys. The site chosen for the factory, at Issoire, was at an equal distance from all of France’s frontiers. A semi-public company, the S.C.A.L., in which the State held 51 per cent of the capital, was created for this factory, the design of which was commissioned from the architectural agency of the Perret brothers. Eight workshop buildings were originally planned, seven of them designed by the Perrets between December 1939 and June 1940. Only two of them were actually built according to these plans. The Occupation scaled down the industrial project and the Perret brothers had nothing more to do with the factory after 1940. Nonetheless, the S.C.A.L. took over and completed the factory in 1950, the new buildings still strongly inspired by the Perret ’s aesthetics. The original brief, drawn up by the S.C.A.L., gave the architects the buildings’ dimensions and heights. Their contribution, from the outset, was therefore primarily concerned with the outer envelope sheltering the machines, and their foundations. The plans produced by the S.C.A.L. show how the industrialists had assimilated the architects’ essential concepts. The constructional system elaborated by the architects found expression, in particular, in a reinforced concrete post and beam structure. At Issoire, the sheet metal rolling shop offers a good illustration of his structure and, in its hierarchy of elements, shows the functional and demonstrative design concept of the Perret brothers at its best. The Issoire factory is a perfect representation of Auguste Perret ’s ideas of how an industrial plant should be monumental, a building conceived more for the machine than for the worker and realising the notion of a «sovereign shelter ».