Willy Breitling, grandson of the founder Léon Breitling, took over the family company in 1935 after the death of his father Gaston, and led it for more than four decades. The year before, in 1934, the firm had added a second independent push-piece for resetting the chronograph, giving the wrist chronograph its modern two-button form, which was quickly adopted across the industry.
Under Willy Breitling the house became a specialist supplier to aviation. In the early 1930s it had begun making cockpit chronographs, which equipped aircraft including Royal Air Force fighters in the Second World War. The Chronomat, with a circular slide rule, followed in 1942, and the Navitimer, whose bezel slide rule could perform the calculations of air navigation, was launched in the early 1950s; Scott Carpenter wore a 24-hour version on his Aurora 7 orbital flight in 1962. In 1969 Breitling, with Heuer, Hamilton and Dubois-Dépraz, presented one of the first self-winding chronograph movements.
Seriously ill and worried by a difficult economic climate, he reluctantly decided to sell. His sons Alain and Gregory were refused a role in the business, according to French Wikipedia. The La Chaux-de-Fonds factory closed in December 1978, and Willy Breitling died in May 1979, the year Ernest Schneider bought the brand.