t the beginning of the 20^th century, the rise of aviation profoundly transformed the requirements for measuring instruments. As aircraft gained in speed and range, navigation became a science of precision in which every second counted. Pilots, confronted with speeds approaching 300 feet per second, had to measure with accuracy the time intervals between various geographical landmarks such as mountains, rivers or railway lines.

In this context, the pocket watch quickly reached its limits. Impractical and difficult to access, it did not meet the constraints of a moving cockpit. As early as 1911, Longines anticipated this evolution by developing wrist chronographs specifically designed for pilots – a bold innovation at a time when the wristwatch was still perceived as a feminine accessory and remained marginal.

The real technological leap came in the 1930s with the emergence of the flyback chronograph. Its principle was revolutionary: where a traditional chronograph required three operations – stop, reset, restart – the flyback made it possible to perform these three actions with a single press of the lower pusher.

This simplification radically transformed in-flight use. It reduced the risk of human error, accelerated decision-making and enabled pilots to recalculate their trajectory in real time. In an environment where the slightest approximation could result in a drift of several kilometres, the flyback became an indispensable ally.

Introduced in a model as early as 1934 and protected by a patent filed on 12 June 1935 and published in June 1936 for a duration of 15 years, this innovation gave Longines a considerable and lasting strategic advantage.

Longines ref. 4974, production date November 1942. Waterproof case and pushers, 13ZN flyback calibre, 18 jewels, column wheel, shock-resistant, Glucydur balance, anti-magnetic. Case: 37.5 mm diameter, stainless steel, screw-down caseback.

From the pioneering 19.73N calibre to the experimental 15’’’ and 13.33Z calibres

If the flyback appears as a breakthrough, it is in fact part of a long tradition of innovation. As early as 1911, Longines laid the foundations of its expertise with the 19.73N calibre. Derived from 19th-century pocket watch movements, this calibre was entirely rethought for the wrist, incorporating a column wheel, a 30-minute counter and an instantaneous jumping mechanism.

Longines ref. 4974, 13ZN flyback calibre, production date November 1941.

Under the impetus of visionary engineers such as Alfred Pfister, the winged hourglass manufacture engaged in a constant quest for miniaturisation and performance. This dynamic continued in the 1930s with the development of the 15’’’ calibre (based on a modified 15-line Valjoux), produced between 1934 and 1936 and used as an experimental platform for the flyback, followed by the 13.33Z calibre.

The latter marked a decisive stage. Highly sophisticated, it was equipped with a column wheel as well as an instantaneous jumping minute counter and served as the basis for testing the flyback mechanism as early as 1935. It represented a major technical challenge, notably due to the “under load” reset (when the mechanism is running).

The 13ZN: birth of a horological legend

These successive developments culminated in the 13ZN calibre, launched in 1936. The first flyback movement produced in series, it was more compact, more robust and better suited to professional use than its predecessors, and quickly established itself as a benchmark.

Technically, the construction of the 13ZN calibre is based on a classic column-wheel architecture, ensuring reliability and smooth operation. The flyback mechanism – integrated rather than modular – operates with fluidity.

Aesthetically, the 13ZN stands out for the quality of its finishing and illustrates the manufacture’s expertise in this field. Combined with innovations such as the waterproof “mushroom pushers” patented by Longines in 1938, the 13ZN equipped models designed to withstand the most demanding conditions.

The flyback patent, application filed on 12 June 1935 and patent registered on 31 March 1936.

Harmonious and recognised for the subtle balance it achieves between precision, robustness and aesthetics, the 13ZN calibre is often regarded by collectors as one of the most accomplished chronograph movements. This is evidenced by the exceptional prices recently achieved at auction by models equipped with the 13ZN.

A reference 4270 piece (“mushroom pushers”) was sold on 7 November 2022 in Geneva for 182,000 Swiss francs, far exceeding its estimate of 20,000 to 40,000 francs. As the piece was not associated with a celebrity, it was the authenticity and history of the watch, confirmed by Longines archives, that justified this exceptional price. Other recent auctions have seen reference 4974 “Tre Tacche” pieces (with a waterproof screw-back case) reach prices ranging between 60,000 and 110,000 dollars, illustrating the technical, historical and aesthetic significance of this watch.

Through the 13ZN calibre and the models that embodied it, Longines undeniably left its mark on the history of watchmaking and helped write that of aviation, on the wrists of pioneers such as Jackie Cochran, Richard Byrd and Howard Hughes. A legacy that, ninety years later, fascinates collectors all the more as it was produced for only around fifteen years.

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FURTHER READING

Longines celebrates its watchmaking icons with a new book

Longines publishes Watches That Made History, a 288-page work by journalist and expert Pierre-André Schmitt, the result of close collaboration with the brand’s Heritage team and collectors from around the world.

The book presents 50 emblematic watches, associated with the achievements of figures such as pioneering aviators Jackie Cochran and Charles Lindbergh, Nobel Prize–winning physicist Albert Einstein, actor-singer Yves Montand and boxing champion Joe Louis.

“Since its origins, Longines has distinguished itself through bold decisions, a pioneering spirit and the determination to stay one step ahead,” recalls Patrick Aoun, CEO of the brand. Daniel Hug, Head of Heritage, adds that “the human dimension of the book helps to understand how, for each of their owners, owning a Longines watch was often instrumental in the success of their achievements.”

Pierre-André Schmitt adds: “Each piece tells a fascinating story or historical context, revealing the impact of Longines watches on aviation, sport and science.” Illustrated with 400 previously unpublished documents, the book offers a deep dive into the technical and human history of Longines, highlighting the innovation, elegance and pioneering spirit that have defined the winged hourglass brand since 1832.