A UNIQUE PATEK PHILIPPE PROTOTYPE STAINLESS STEEL QUARTZ BRACELET WATCH
Prototype Nautilus with a Sigma Dial.

Brand: Patek Philippe
Model: Nautilus Sigma Dial
Case reference: 3900
Year: 1980's
Movement: Quartz
Dial: Sigma Dial, blue, 18k white gold applied hour markers, 18k white gold hands, blued centre seconds hand, date aperture at the three o'clock position
Material: Stainless steel
Bracelet/Strap: Stainless steel bracelet
Signed: Dial, movement, case, bracelet
Dimension: 33mm
Accessories: Patek Philippe travel pouch

Patek Philippe Nautilus Ref. 3900 Prototype – A Rare Piece of Manufacture History

A truly exceptional and historically significant timepiece, this Patek Philippe Nautilus Ref. 3900 stands apart as a prototype directly from the Patek Philippe manufacture—a piece that was never meant for commercial sale.

In 1976, Patek Philippe introduced the Nautilus, a luxury sports watch designed by Gérald Genta, breaking conventions with its bold, stainless steel case and integrated bracelet. Inspired by maritime aesthetics, Genta modelled the case after a ship’s porthole, complete with lateral hinges that evoked the look of a watertight seal. Upon its release, the Ref. 3700/1, often nicknamed the “Jumbo,” was met with skepticism—luxury watches were traditionally crafted in gold, and a steel sports watch at a high price point was unprecedented. However, over time, the Nautilus became one of the most coveted watch designs in history.

As demand for the Nautilus grew, Patek Philippe recognised the need for a more versatile, midsize version of its flagship model. In the early 1980s, the brand introduced the Nautilus Ref. 3900/1, a 33mm alternative to the 3700, designed for those who wanted the elegance of the Nautilus in a smaller, more wearable format. Unlike its larger predecessor, the 3900 featured a quartz movement, reflecting the growing interest in precision timekeeping during the Quartz Revolution.

This particular example, however, is no ordinary Ref. 3900. When contacted, Patek Philippe confirmed its authenticity and unique origin—a prototype produced at their manufacture, likely intended for one of their watchmakers for internal use. It bears no serial numbers on the case or movement, as it was never meant for commercial sale, making it an exceptionally rare piece of Patek Philippe history.

One of the defining features of this watch is its Sigma dial, identified by the ⍬ symbols flanking “Swiss” at 6 o’clock. The use of Sigma dials was introduced in the 1970s by the Swiss watch industry to emphasise the use of solid gold components for the hour markers and hands, a subtle yet prestigious hallmark of quality and craftsmanship. The designation was promoted by the Association pour la Promotion Industrielle de l’Or (APRIOR), a collective of leading Swiss watch brands—including Patek Philippe, Rolex, and Vacheron Constantin—who sought to distinguish timepieces that incorporated gold in their dials.

While Sigma dials were most commonly found on gold or bi-metal watches, their appearance on a stainless steel Nautilus is exceedingly rare. The juxtaposition of a steel sports watch with gold markers reflects an era when Swiss watchmakers were navigating the Quartz Crisis, balancing luxury with innovation.