Following the Royal Italian Navy's approach to them and other watch brands in 1935 to build a watch that was highly water-resistant and legible in unfavourable conditions, Panerai began the development of a divers watch. In 1936 Panerai developed 10 prototype watches and submitted them for testing. This prototype was called the Radiomir, after the radioactive substance used to paint its hands and indices. Production of the watch for use by the military began in 1938 with Panerai adhering to strict guidelines from the Italian Navy – a long water-proof strap wearable over a diving suit, a hand-wound mechanical movement, luminescent indices and numerals and a large dial. With movements sourced through Rolex, the ref. 3646, which is what we have here, is powered by the manual-wind Cortébert-made cal. 618, which was originlly a pocket watch movement. Fitted with radium-filled sandwich dials that were made by the Arturo Junghans watch factory in Venice. Known as an anonymous variant due to its lack of branding at 12 o’clock, this Type-D example was likely worn by the Kampfschwimmer around 1943.