Since the autumn of 1938, the needs of the Royal Italian Navy for underwater watches increased strongly and Panerai supplied the “Radiomir”, which progressively underwent a series of modifications. The major revolution of those years was the way in which the dial was constructed. This went from a single plate with the markers and numerals engraved on it and literally filled with self-luminous paste, to the creation of the so-called “sandwich” dial. With the aim of achieving greater luminosity, this dial designed by Officine Panerai was initially made of three parts. The upper plate was drilled and the lower plate, which was solid, was covered with luminous substance (Radiomir and later Luminor). The upper and lower plates were joined with the interposition of a transparent Perspex® disc to perfectly protect the self-luminous paste. In this way the dial could contain a large quantity of the selfluminous substance. The watch was so luminous that - during night operations - the underwater commandos had sometimes to cover the dial with mud or seaweed in order to avoid being spotted. The sandwich construction has been progressively further adjusted and is currently made of only two superimposed plates. To achieve the optimum level of luminescence and the best endurance over time, Panerai uses today the Swiss Grade A Super-LumiNova®, a substance consisting of special highly-performing pigments.