The present watch is part of a small series of large aviator's watches developed by A. Lange & Söhne around 1940 and exclusively reserved for the German Airforce, following strict specifications in regard to accuracy. Movement caliber 48 was fitted with an indirect sweep center seconds mechanism with hacking feature based on Junghans' patent, hence renamed 48.1. The balance is stopped and hands can be set while simultaneously depressing the button in the band and pulling the large crown. The large size of the crown allows winding and setting even while wearing gloves.
The present watch is from a series of observation watches made for the Waffen-SS, also fitted with the calibre 48.1 movement but with a different dial layout. For photographic purposes the seconds scale was mirror-inverted. Following the first prototypes with silver cases, Lange was to supply 10 examples with nickel-brass cases each month. There appear to have been very few pieces produced as prototypes, making the present watch a truly rare find.
The models are explained and illustrated in Reinhard Meis, A. Lange & Söhne - eine Uhrmacher-Dynastie aus Dresden, pp. 220 & 221 and in Konrad Knirim, Military Timepieces, p. 452.