The Beobachtungsuhr, or B-Uhr (“observation watch”), was the navigation wristwatch of the German Luftwaffe. In 1940 the Reich Air Ministry (RLM) set out its requirements in construction specification Fl. 23883 and obliged several makers to produce it to strict rules. The watch has a 55mm case, usually steel with a snap-on back, sized to hold a large pocket-watch-type movement, and an oversized onion crown that could be used with gloves on. The manually wound movement drives central seconds with a stop function for exact setting, and an inner iron cage protects it from magnetism. The black dial carries luminous numerals and sword hands, with a triangle flanked by two dots at 12. The specification number Fl. 23883 is engraved on the side of the case band, and the inside of the case back records the type, device number, movement and maker. It matters because its layout is still the basis of the Flieger watches made by several of the original suppliers today.

Five firms produced B-Uhren during the war: IWC in Schaffhausen, the only Swiss maker, with its calibre 52 T.S.C. in the reference 431; Stowa and Laco of Pforzheim; and Wempe and A. Lange & Söhne in Glashütte. Two dial patterns exist: the early “Baumuster A” with large Arabic hours 1 to 11, and the later “Baumuster B” with five-minute numerals on the outer ring and the hours on a small inner ring. Despite the “pilot’s watch” label, the B-Uhr was mainly worn by the navigators on board, who used it with an octant to fix the aircraft’s position, while pilots often wore chronographs as a back-up. The long leather strap allowed the watch to be worn over a flight jacket.

Auction houses describe original B-Uhren as rare military and historical relics, and prices vary widely with maker, condition and documentation. A 55mm A. Lange & Söhne example sold on 10 October 1941, with certificate and copy of the original receipt, made HK$75,625 at Bonhams Hong Kong in 2019, while a 1940 IWC reference 431 sold for HK$237,500 at Phillips. Antiquorum has sold other Lange examples in New York for far lower sums, between about USD 4,400 and USD 8,750. The original B-Uhr is no longer produced for military use, but the design lives on: Laco and Stowa still make Flieger watches based on it, including 55mm replicas, and IWC continues the line with its Big Pilot’s Watch.