The adventure of the pilot’s watch (II)

The rise of civil aviation in the 1920s and 1930s, alongside exploits by such legends as Mermoz, Lindberg, Saint Exupéry, Nungesser and Coli, placed the onus on watchmakers to provide more advanced timekeeping. An instructor at the US Naval Academy in Annapolis, Philip Van Horn Weems would make an important contribution to this. He observed that delayed calculations combined with imprecise timing could have sometimes fatal consequences in flight. After all, at 200 mph a plane travels one mile every 18 seconds (that’s 1.6 kilometres at 320 kph). In 1929 Weems filed a patent for a wristwatch he had devised, in consultation with Longines Wittnauer, that would complement the bulky chronometers on the instrument panel. His invention allowed pilots to synchronise their watch to the second, without having to adjust the hands, using a radio-transmitted signal and a graduated rotating inner dial.

The first hour angle watch

Watches at that time had no stop-seconds mechanism and for this reason couldn’t be adjusted with sufficient precision to calculate position at high speed. Philip Van Horn Weems’ design was reprised by Charles A. Lindbergh, Weems’ pupil and first to make a non-stop solo flight across the Atlantic, in 1927. Lindbergh also entrusted his idea to Longines for development; the result was the first hour angle watch with rotating bezel and dial. Used in conjunction with a sextant and flight charts, Lindbergh’s watch could be used to calculate longitude which, paired with latitude, gives a precise geographic location. The patent was filed in 1935. The following year, Longines invented the flyback chronograph thanks to which pilots could stop, reset and instantaneously start measuring a new interval with a single press of the pusher.

The chronograph would join the instruments on-board fighter planes, but only after being put through its paces in a series of stringent tests. Like a chronometer, a chronograph had to prove its worth, not least in temperature conditions ranging from -30°C to +40°C. Any watch that showed a variation in rate of more than 45 seconds over three consecutive days was declared unfit for service, and returned to the workshops to be inspected and adjusted. It was also tested for resistance to vibrations, sudden acceleration and deceleration, as well as shock-resistance. Electro-magnets were used to check it would withstand magnetic fields inside the cockpit. To test water-resistance, the watch was sprayed with a mist and placed inside a tank to simulate a humid tropical climate.

The legendary B-Uhren

Eminently simple, these instruments were designed so that pilots could use them while wearing gloves and read time accurately at a glance. Indeed, their movements could easily have qualified as chronometers, such was their precision. Not that there was room on the dial for superfluous inscriptions of any kind. Several manufacturers became fixtures of the aviation world and supplied timepieces to national air forces as the Second World War loomed. As mentioned earlier, Zenith received commissions from the French Armée de l’Air for Type 20 Aéronef watches. Omega, Longines, Cyma and Jaeger-LeCoultre supplied the British Royal Air Force. As for Hanhart, Tutima, A. Lange & Söhne, Stowa, Berg, Aristo, Laco, Wempe and IWC, from 1935 they fulfilled orders from the German Luftwaffe which issued its pilots with chronographs, navigating crew with three-hand watches, and bomber navigators with observation watches: the legendary B-Uhren.

Between 1940 and 1945, five manufacturers were assigned to supply the Luftwaffe with these B-Uhren. They were A. Lange & Söhne, IWC, Laco, Stowa and Wempe. Each watch was produced to specifications: 55mm diameter, oversized diamond or onion crown, black dial with luminescent white Arabic numerals, a luminescent arrow marker at the 12 position and luminescent blued hands. The chronometer movement was certified by the Hamburg Observatory and must be fitted with a stop-seconds mechanism and a Breguet balance spring. The strap had to be long enough for the watch to be worn over a flight jacket.

Many of the names that contributed to the golden years of aviation still perpetuate the tradition, including Longines, Omega and Zenith. Looking specifically at the companies which manufactured the Luftwaffe’s B-Uhren, neither A. Lange & Söhne nor Wempe has any equivalent in its catalogue today. The Big Pilot by IWC, on the other hand, is clearly a contemporary iteration. Stowa, under watchmaker Jörg Schauer, continues to pay tribute to these early observation watches, as does Laco. Though it would be difficult to ignore the context in which the B-Uhr earned its fame, as a watch made for use in extreme conditions it represents a rarely equalled combination of manufacturing and design.