THE FIRST ROYAL OAK CASES

The case of the Royal Oak 5402 is sometimes described as a monocoque. What does that mean? Published by Albert Berner in 1961, The Illustrated Professional Dictionary of Horology explains that a watch case has two functions. The first is to protect the precious and fragile mechanical watch movement against dust, damp and shocks. The second is to “give the watch as attractive an appearance as possible, subject to fashion and the taste of the public.”

The author then explains that the case of a wristwatch is usually composed of three main superimposed elements: the caseback, the case middle and the bezel. Rubber seals fitted between each of these levels ensure water resistance. This structure is known as a "three-piece" case. While Albert Berner did not define the monocoque case, he introduced a category that prefigured it: the "two-piece" wristwatch-case in which the lugs and case middle merge to form a single component. This structure reduces the risk of moisture penetration, makes the case more rigid and sometimes allows it to be slimmed down while maintaining access to the movement through the back of the watch.

At Audemars Piguet, “two-part” wristwatches appeared as early as the 1920s. They are notably found in many Art Deco rectangular watches, several of which are detailed in the book Audemars Piguet’s 20^th Century Complicated Wristwatches. In Pre-Model 182 (pictured) introduced in 1982, the bezel blends into the case middle for aesthetic reasons and the back opens on a hinge. Thirty years later, the bezel of Model 5115 seems to be detached from the case middle, but is an integral part of it for water-resistance reasons.

While the Royal Oak’s bezel is often described as octagonal, it is far more than that. Its centre is a circle, while its periphery is a rounded octagon, vertically satin-finished and strongly bevelled. The 40-degree bevel perfectly follows the bezel’s octagonal-rounded shape and results in a thin satin-finished edge. A lapping machine helps create a mirror-polished surface highlighting the traditional technique of bevelling (chamfering). Seen from the front, it takes up almost a quarter of the bezel's surface and links the moiré reflections of the Tapisserie dial to the facets of the tapered bracelet.

At each corner of the eight curved facets that punctuate the bezel, a hexagonal hole is made to accommodate a screw. Until then, in the watchmaking tradition, watch bezels had sometimes featured hour-markers, either at 12, 3, 6 and 9 o'clock, or at each hour. In the same tradition, the screws securing cases were always hidden. Gérald Genta departed from these two practices and structured the circumference of the bezel in eight elements independent of the dial since it was impossible to follow the hours graduation. Further freeing himself from the shackles of convention, he punctuated the bezel with visible fastening screws. Note as well that for aesthetic reasons, he decided not to put a screw in the classic 12 o’clock position. In short, Genta designed a bezel driven by its own dynamics and aesthetic rhythms, independent of those on the dial yet echoing the case and bracelet’s design and sensitivity to light.

With a maximum thickness of two millimetres, the inside of the Royal Oak “Jumbo” bezel is partially hollowed out to make room for the water-resistance seal. A small undercut is made for the heel of the sapphire crystal to rest on. Water-resistance is ensured when the case is closed and the seals are pressurised.

The eight hexagonal screws punctuating the octagonal bezel were perhaps the most disruptive element of the 1972 Royal Oak. The advertisers of the 1970s and 1980s were well aware of this, humorously using this non-conformity as an argument for differentiation: “A price like that, he teased, and they don’t conceal the screws?”

The slot of the screw heads suggests that they can be turned with a screwdriver, whereas their shape indicates the opposite. Indeed, the fact that they are embedded in the hexagonal openings of the bezel means they are unable to rotate – in other words, these are screws that do not even turn! Some have seen in them the symbol of the case’s resistance, making it a kind of inviolable safe containing a mechanical treasure: Calibre 2121.

The secret of this system lies in the fact that the hexagonal screws are fitted with round nuts introduced from the back of the watch and which serve to close it.

Nonetheless, although this system protected the movement perfectly, it did not prevent water from seeping down the screws and nuts. Wilfred Berney, founder of the Audemars Piguet Customer Service department, lived through the early years of the Royal Oak. He says that the screws of the first 300 Royal Oak watches were made of steel. Seawater would trickle in along the screws and deposit its salt, "attacking and corroding indiscriminately. The result was appalling and Genta's famous ‘diving helmet’ was blocked... Penetrating oils and other such products could be used to help remove the case screws, but that did not work at all for the bracelet screws. The only way to resolve the situation was to produce special drill bits and a whole set of tools to drill these screws, to reach the part where the bracelet pivots and then make it drop off using ultrasound technology.” These incidents led to Royal Oak screws being made in white gold.

Since 1972, while remaining true to itself, the Royal Oak has been perpetually renewed. It has been interpreted in more than 550 models. Its diameter has varied from 20 to 44 mm and its thickness from 6.3 to 15 mm. It has been clothed in steel, gold, tantalum, ceramic, titanium and platinum, and even covered in diamonds. It has been fitted with all the classic horological complications, from the perpetual calendar to the chronograph, including the tourbillon, the minute repeater and the Grand Complication.

These transformations have been accompanied by countless technical developments. The watch exterior components have been rethought, redesigned and improved countless times. Among those that have changed the least are the eight hexagonal screws. They have always remained through-type screws, with a few exceptions (e.g. the pocket watch variant 5691, certain examples of Models 5554, 25729 or 25860), while the hexagonal upper part has always played the role of a nut, except on rare occasions when they have a simple decorative role (e.g. model 15300). Above all, they have remained in white gold, even if the improvement in the quality of the steel would undoubtedly have made it possible to use this material as had been imagined in 1972. 

The crown has also retained its hexagonal shape. Its main aesthetic evolution is due to the addition of an AP engraving, which was introduced at the end of the 1990s and became the norm in the 2000s. On the other hand, the screw-lock crown was adopted in the early 1980s because it reduced the risk of mishandling, particularly when immersed in water. It appeared in 1983 in Models 4332, 5572, 5584, 5658. In 1990, it was added to the 14700 family of models, followed by its direct descendants 15300 (from 2005), 15400 (from 2012), and 15500 (from 2019). In this system, the main seals are fixed to the case, so that they can be replaced independently of the crown. Despite their significant advantages, screw-lock crowns have not been fitted to all Royal Oak watches. They proved to be incompatible with certain calibres (e.g. 2121, 2120, 2835, etc.) and sometimes affected the winding system. This has meant that no ultra-thin Royal Oak 39 mm watches have ever been fitted with them.

We could go on and on with the list of case redesigns. We will simply conclude by adding that the "three-part" model became established in the 2000s, having been notably reintroduced in the Royal Oak Grand Complication 25865 in 1997 and in the first Royal Oak Chronograph 25860. Since then, this case has been fitted to the vast majority of models, including the classic Models 15300, 15400 and 15500, as well as the 15202 and the Royal Oak 16202 launched in 2022.

This overview of the few transformations of the Royal Oak case sheds light on the complexity of its case and the challenges it has constantly posed. It shows the extent to which an iconic watch – sometimes thought to have remained unchanged and timeless – is in fact the object of constant research. Among the latest innovations, one need only mention the Royal Oak Selfwinding Perpetual Calendar Ultra-Thin 26586 (2019), which uses the dial as an upper movement bridge, or the architectural design of the Royal Oak Minute Repeater 26591 (2021), whose Supersonnerie case amplifies sound by means of a purpose-built “soundboard”.