With IWC Extract from the ledger dated 5 November 2009 confirming the sale of the present watch on 11 October 1940 to Siegfried Heindorf, Berlin.
An example of the "Big Pilot's Watch" is on permanent exhibition at the prestigious IWC Museum in Schaffhausen. The 'biggest' IWC pilot's watch was supplied to the German Luftwaffe in 1940 in an edition of 1,000 examples. The 'big device' constructed according to the criteria for observer's watches with the pocket watch calibre 52 T.S.C. is the biggest wristwatch ever built by IWC, with a case diameter of 55 mm., a height of 16.5 mm. and a weight of 183 grams. The extra long wrist strap with double bow and clasp clip makes it possible to wear the watch over a flying suit.
In 1940, IWC produced 1200 examples of their calibre 52 19''' H 6 S.C. movement, numbered 1'013'801 to 1'015'000 out of which 1000 examples were used for "Die grosse Fliegeruhr" or "Big Pilot's Watch", made for the German Air Force, following strict specifications in regard to accuracy. These movements were cased in cases numbered from 1'033'201 to 1'034'200 and shipped to Siegfried Heindorf in Berlin. The movements were fitted with an indirect sweep centre mechanism with hacking feature thanks to which the balance is stopped while the crown is pulled out, thus allowing setting of the time to the split second. The large size of the crown allows winding and setting even when wearing gloves.
The inside of the case backs were engraved with the following military markings:
B-Uhr (for Beobachtungs-Uhr or Navigation Watch)
Bauart (manufacturer): I.W.C.
Werk Nr. (movement no.):
Anforderz. FL 23833 (classification number)
As of around 1937, watches used by the German Air Force were fitted with such a panel indicating manufacturer, serial number and a "Fl" number. In order to disguise information regarding manufacturer and quantities produced, these indications were coded from 1941 onwards.
The watches were primary tested by the Deutsche Versuchsanstalt fr Luftfahrt DVL (German Aviation Research Institute) and classified with a so-called "Fl.-Number". The Fl. stands for flight and the first two digits, 22, for flight control; 23 stands for navigation and 25 for radio surveillance, followed by the three digits serial number given by the DVL.
For a description and illustration of the model supplied by IWC see Military Timepieces by Konrad Knirim, pp. 351 - 352 and Die Fliegeruhren von IWC by Rüdiger Bucher and Christian Pfeiffer-Belli, pp. 73 - 81.