Established in 1875 in the Swiss village of Le Brassus, Audemars Piguet has earned a distinguished reputation as a premier watchmaker. The brand is renowned for its heritage of craftsmanship and relentless pursuit of innovation. Celebrated as one of the most legendary watch designs ever, Audemars Piguet Royal Oak has secured its rightful place in horological history. From quartz's precision to the perpetual calendar's complexity, each evolution reflects innovation and craftsmanship. This blog explores the transformation of the Royal Oak’s movements, tracing its journey from groundbreaking quartz technology to haute horology’s pinnacle of mechanical mastery.

The Quartz Crisis & Audemars Piguet’s Mechanical Rebellion

The Quartz Crisis of the 1970s marked a turning point in watchmaking, as battery-powered quartz movements threatened traditional Swiss mechanical watches. Many historic watchmakers faced bankruptcy, and the industry saw widespread job losses.

Despite this turmoil, Audemars Piguet (AP) refused to abandon mechanical innovation. Rather than competing on price with mass-produced quartz models, AP doubled down on its expertise in high-end mechanical watchmaking. The launch of the Royal Oak in 1972—an avant-garde luxury sports watch with an ultra-thin automatic movement—was a bold move. 

The Evolutionary Changes of Movements in the Royal Oak

1. Calibre 2120: The Foundation of Royal Oak’s Success

 The World’s Thinnest Full-Rotor Automatic Movement (2.45mm)

The original AP Royal Oak models featured the calibre 2121 movement, an evolution of the calibre 2120 that Audemars Piguet introduced in 1967. At the time, the calibre 2120 held the distinction of being the thinnest, self-winding, with date function, measuring just 3.05mm in height. The calibre 2121 further enhanced this design with a Gyromax balance (an adjustable-mass balance wheel used in mechanical watches to improve timekeeping accuracy) and an advanced anti-shock system. These are all encased in a highly robust metal structure that ensures exceptional durability against strong impacts. 

For several decades, co-developed by LeCoultre & Cie, Audemars Piguet, and Vacheron Constantin, this mechanical movement held the title of the world’s thinnest automatic calibre with a central rotor, measuring just 2.45mm thick. Besides, its groundbreaking engineering allowed for ultra-thin case designs without compromising reliability. 

Peripheral Rotor Design

Unlike traditional automatic movements with a centrally mounted rotor, the Calibre 2120 featured a peripheral rotor. A key feature is its 21-carat oscillating weight, which moves along a circular track on ruby rollers. This innovative design reduced thickness, enhanced winding efficiency. In this way, it maintained an unobstructed view of the movement’s beautifully hand-finished components.

The Base for Future Complications

The ultra-thin design of the Calibre 2120 provided a strong base for adding modular complications. This allowed for the creation of perpetual calendars, skeletonised versions, and other high-end watch features for the upcoming models. Its slimness allowed watchmakers to incorporate intricate mechanisms without significantly increasing case size.

2. The First Perpetual Calendar Movement in the Royal Oak (1978–1984)

Six years after introducing the Audemars Piguet Royal Oak, the brand launched the calibre 2120/2800. It reignited industry-wide enthusiasm for traditional complications and inspired further innovation in watchmaking.

Calibre 2120/2800 (Ref. 5548 & Ref. 5554):

Measuring just 3.95mm, it combined AP’s ultra-thin Calibre 2120 with a perpetual calendar module by Dubois-Dépraz (complications specialist). It features a 12-month program wheel and a Maltese cross leap year mechanism for precise date tracking. Unlike bulky traditional complications, this innovation allowed for an elegant, slim profile, reinforcing AP’s mechanical expertise. Released in References 5548 and 5554, this movement symbolised Swiss resilience against quartz watches.

3. The 1990s: Refining the Perpetual Calendar Movement

1995: Caliber 2120/2802 (Ref. 25810) – The Return of the Leap Year

In 1995, Audemars Piguet introduced the Caliber 2120/2802 in the Royal Oak Perpetual Calendar Ref. 25810.  The return of the leap year display has been marked—a crucial enhancement for precision and usability. Earlier, perpetual calendars required careful tracking of leap years manually. By adding a dedicated leap year indicator, AP improved readability and ease of adjustment. 

Additionally, the movement featured coaxial month and leap year hands, streamlining the dial layout while maintaining the Royal Oak’s signature elegance. These improvements ensured that its perpetual calendar watches remained both technically superior as well as user-friendly for collectors.

1997: The Grande Complication (Ref. 25865) – Pushing Limits

In 1997, Audemars Piguet unveiled the Royal Oak Grande Complication Ref. 25865. It was a technical marvel combining a minute repeater, split-seconds chronograph, and perpetual calendar—three of haute horology’s most revered complications. To achieve this, AP extensively modified its ultra-thin Caliber 2120 and integrated multiple layers of mechanisms while maintaining a wearable case profile. The challenge was to make sure the complications worked smoothly together.

However, by mastering this intricate fusion, AP reinforced its status as a leader in high-complication watchmaking. It proved that even within a bold sports watch design, tradition and innovation could coexist effortlessly.

4. The 21st Century: Thinner, Smarter, More Advanced

2015: Caliber 5134 (Ref. 26574) – A New Generation

In 2015, Audemars Piguet introduced the Reference 26574, featuring the Caliber 5134, marking a significant advancement in the Royal Oak Perpetual Calendar lineage. This model debuted in an all-new 41mm case, expanding from the traditional 39mm diameter while maintaining the collection’s signature aesthetics.

A key change in the Caliber 5134 was its increased thickness—from 3.95mm to 4.31mm—due to the addition of a week indicator. It was a rare complication that enhanced practicality. Despite this, Audemars Piguet ensured that the watch’s case remained remarkably slim at 9.5mm. However, it was only slightly thicker than its predecessor’s 9.3mm, preserving wearability.

Another major innovation was the co-planar 12-month and leap-year cam, a patented mechanism that improved perpetual calendar accuracy and efficiency. This movement retained the essential complications—day, date, month, moon phase, and leap-year cycle—while enhancing functionality.

Beyond its technical advancements, the Caliber 5134 powered some of the Audemars Piguet Royal Oak perpetual calendar models of the modern era. These included the black ceramic Reference 26579CE, the black ceramic openworked Reference 26585CE, the white ceramic Reference 26579CB, and the striking blue ceramic Reference 26579CS. More than just a movement, it played a pivotal role in introducing complicated watchmaking to a new generation of collectors. The Royal Oak Perpetual Calendar, with its signature week indicator, captivated an all-new demographic. It drew in high-profile collectors and celebrities such as Jay-Z, Kevin Hart, Ed Sheeran, and Travis Scott. The latter even selected the Caliber 5134 as the base for his exclusive “Cactus Jack” collaboration with Audemars Piguet, further cementing its place in contemporary horology.

2018: RD#2 – The Ultra-Thin Revolution (Caliber 5133)

In 2018, Audemars Piguet unveiled the Royal Oak RD#2 Perpetual Calendar Ultra-Thin, powered by the groundbreaking Caliber 5133. At just 2.89 mm thick, this movement set a new world record as the thinnest perpetual calendar ever created, redefining the boundaries of haute horology.

A key innovation was the integration of a 48-month program wheel, which functioned as both a gear and a cam. By merging components that traditionally existed separately, Audemars Piguet eliminated unnecessary layers. It significantly reduced movement thickness while improving mechanical efficiency.

This design enhanced the seamless operation of the perpetual calendar, ensuring precise date transitions without additional complexity. The ultra-thin architecture not only improved ergonomics but also showcased Audemars Piguet’s mastery of movement miniaturisation. The RD#2 was a testament to the brand’s commitment to innovation, blending advanced engineering with the timeless elegance of the Royal Oak collection.

5. 2024: The Pinnacle of Movement Engineering – Caliber 7138

The year 2024 marked a defining moment in Audemars Piguet’s 150-year legacy with the introduction of the Caliber 7138. 

One of its most groundbreaking features is the four-position crown, a first in Audemars Piguet’s perpetual calendar lineage. This intuitive design allowed for effortless adjustments: winding in position 1, date and month setting in position 2, time setting in position 3, and an additional, cleverly engineered return to position 2 for day and moon phase adjustments. This sophisticated yet seamless operation enhanced functionality while maintaining an elegant, user-friendly experience.

Conventional perpetual calendars typically rely on pushers or specialised tools for calendar adjustments. However, it can be inconvenient and may compromise the case or water resistance of the watch. In contrast, the Caliber 7138 revolutionised this by incorporating an "all-in-one" crown system. As a benefit, users can effortlessly manage all perpetual calendar functions through simple crown manipulation. 

Furthermore, the Caliber 7138 boasts an increased power reserve of 55 hours. It improved upon its predecessor’s 40-hour limit and ensured extended reliability.

Moreover, the Caliber 7138 stands out due to its innovative built-in safeguard.  It prevents adjustments to the indicators during the “no-go” period between 9 p.m. and 3 a.m. In this period, many mechanical movements transitioned their date and other complications. If you try to manually adjust the indicators during this time, it can cause mechanical stress, misalignment, or even internal damage to the watch's gear train. So, this is a significant technical achievement in watchmaking as Caliber 7138 eliminates this risk by automatically locking out any manual changes during this period. As a benefit, the safeguard increases the longevity and reliability of the watch, reducing the need for repairs or recalibration.

The fact that Audemars Piguet spent five years perfecting this movement highlights their commitment to precision, durability, and user-friendliness. 

The Evolutionary Impact of Royal Oak Movements 

The evolution of Royal Oak movements has shaped haute horology in multiple ways:

• Ultra-Thin Revolution – Inspired a new era of slim, complex watches.
  

• Perpetual Calendar Advancements – Enhanced readability, precision, and ease of use. 

• User-Centric Design – Set new standards for intuitive watchmaking.
  

• Cultural Integration – Elevated luxury watches beyond horology, into mainstream culture.

Wrapping Up: The Future of Royal Oak Movements

Audemars Piguet continues to redefine horology by pushing the boundaries of ultra-thin movement design while integrating high complications. The brand’s relentless innovation, fully crown-adjustable perpetual calendars, and precision-enhancing free-sprung balances reflect its commitment to mechanical excellence. 

With a perfect balance of elegance with technical mastery, Audemars Piguet ensures that slim movements do not compromise performance. The Royal Oak remains a benchmark in watchmaking, setting new industry standards in design, efficiency, and craftsmanship. The brand proves that tradition and innovation can coexist seamlessly in the world of haute horology.

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