The Patek Philippe caliber 28-255 C is a refined variation of the legendary ultra-thin automatic 28-255 movement. This caliber is most famously known for powering the early Nautilus Ref. 3700/1A, but the "C" suffix introduces a subtle yet important change: the addition of a calendar (date) function. Like its base caliber, the 28-255 C remains a masterclass in slim automatic watchmaking, representing a key chapter in both Patek Philippe and luxury sports watch history.

Overview of the Caliber 28-255 C

The caliber 28-255 C was launched in the mid-1970s, designed around the original Jaeger-LeCoultre caliber 920 architecture. This renowned ultra-thin movement was used exclusively by Patek Philippe, Audemars Piguet, and Vacheron Constantin—brands considered part of the Swiss "Holy Trinity."

The 28-255 C is a 3.05 mm-thick automatic movement, despite the integration of a date complication, which is a remarkable feat of engineering. It became the beating heart of the Nautilus Ref. 3700/1, also known as the "Jumbo Nautilus"—the first sports watch from Patek Philippe and a piece now recognized as one of the most iconic timepieces in horology.

Technical Characteristics

Despite its age and slender form, the 28-255 C remains a technically accomplished movement, with outstanding finishing and performance.

Key specs include:

• Type: Ultra-thin automatic movement with date

• Diameter: 28.0 mm

• Height: 3.05 mm

• Jewels: 36

• Frequency: 19,800 vibrations per hour (2.75 Hz)

• Power Reserve: ~40–42 hours

• Rotor: 21k gold, mounted on ball bearings

• Calendar: Instantaneous date display, typically at 3 o’clock

• Balance: Free-sprung Gyromax

• Shock protection: Yes, with an Incabloc-style system

The ultra-thin rotor mounted on ball bearings allows for efficient winding without increasing the movement’s overall height. Its date mechanism is seamlessly integrated, preserving the movement’s balanced architecture.

Aesthetics and Finishing

The 28-255 C upholds Patek Philippe’s highest standards of decoration. Even though it is usually hidden behind a solid caseback (as in the Nautilus 3700/1A), it features:

• Côtes de Genève on the bridges

• Perlage on the mainplate

• Anglage (beveled edges) on all bridges and components

• Polished screw heads and carefully heat-blued components

The rotor, made from 21k gold, often features subtle engraving and fine brushing.

Use in Patek Philippe Watches

The Nautilus Ref. 3700/1A is the most notable watch to house the 28-255 C. This model launched in 1976 and marked Patek Philippe’s entry into the luxury sports watch market, following Audemars Piguet’s Royal Oak.

Other references powered by the 28-255 C are extremely rare, as this movement was highly specific and produced in limited quantities before being phased out in favor of in-house calibers like the 335 SC and later the 324 SC.

Collectibility and Historical Importance

The 28-255 C is no longer in production and has become highly collectible, particularly when found in original Nautilus models. Collectors view it not just as a beautiful mechanical movement, but as a piece of Swiss watchmaking history.

It represents a time when watchmakers pushed the limits of what automatic movements could achieve—ultra-thin design, integrated complications, and full rotor efficiency, all in a luxury steel watch.

Servicing and Rarity

Servicing the 28-255 C requires an expert hand. Due to its thinness, precision parts, and rarity, it must be handled by master watchmakers—ideally those with experience in vintage Patek Philippe movements. Replacement parts are scarce, making preventive maintenance critical.

Despite these challenges, well-maintained examples of this movement remain reliable and accurate, often lasting decades with proper care.

Conclusion

The Patek Philippe caliber 28-255 C is more than a movement—it is a milestone in the evolution of luxury sports watches. As the powerhouse behind the original Nautilus with date, it brought together technical innovation, slim profile, and elite Swiss craftsmanship. Today, it remains a symbol of Patek Philippe’s ability to merge tradition with bold design, earning its place in the pantheon of horological greats.