Ultra-Slim: The Lesser Known Side of Audemars Piguet

Today Audemars Piguet is synonymous with the Royal Oak, perhaps only overshadowed by the success of the Royal Oak Offshore. Yet while the idea does not immediately come to mind, Audemars Piguet also has a great reputation for ultra slim watches.

A Pioneer in Ultra-Thinness

This reputation started in 1938, when they introduced the manual wind movement cal. 9ML, with a thickness of only 1.64mm. This movement did not come completely out of nowhere, since Audemars Piguet was already famous for ultra-slim movements for pocket watches. In 1921 they introduced a pocket watch movement that was only 1.32mm thin. Courteous rivalry back then was common in the field of ultra-thin movements, and this Audemars Piguet movement was a response to the introduction in 1907 by Jaeger-LeCoultre of a 1.38mm thin pocket watch movement.

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Audemars Piguet coin watch powered by Caliber 9ML

But it wasn’t all rivalry. Despite being a stunning movement, with perfect anglage and tiny perlage in even the smallest places of the main plate, cal. 9ML remains a rare bird and 772 were sold during the 15 years when it was part of the Audemars Piguet collection. Although Audemars Piguet offered the movement in a regular ultra-thin wristwatch, there was also a coin watch fitted with this movement.

Perhaps it was a time when WWII had just ended, and large parts of the world were still scarred, making demand a possible issue. This didn’t stop Audemars Piguet though from continuing the path of ultra-slim movements for wristwatches.

1950s: Collaboration

The next step was taken in 1953 when Audemars Piguet introduced calibre 2003, also a manual wind movement. This calibre was developed together with Jaeger-LeCoultre with involvement of Vacheron Constantin. Based on the cal. 9ML, calibre 2003 shares the main characteristics such as height and diameter, but the number of bridges were reduced. The main goal for this was to make the movement sturdier.

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Caliber 2003: less bridges increased the sturdiness of the movement

Since Audemars Piguet supplied the base movement for the project, it retained the exclusive right to produce and market calibre 2003 for the next two years. In 1955 Vacheron Constantin introduced the calibre as 1003, and both brands kept the movement in production until late 2002, early 2003. Jaeger-LeCoultre though went a different path. Although the movement did get a Jaeger-LeCoultre designation, as calibre 803, it was never used in any Jaeger-LeCoultre up for public sale.

1960s: Going Automatic

In the 1960s Audemars Piguet embarked on a quest together with Vacheron Constantin, Jaeger-LeCoultre and Patek Philippe to create a reliable, ultra-thin automatic movement. The result was presented in 1967 as calibre 2120. This movement only has a height of 2.45mm and was destined to power the most legendary watch in Audemars Piguet’s history: the original Royal Oak.

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Caliber 2120/2121 can even today still be found in the Jules Audemars Extra Thin and Royal Oak Extra Thin

When the Royal Oak was introduced in 1972, it was fitted with calibre 2121. Based on calibre 2120, which is a time only movement, it was fitted with a date complication. This increased the overall height of the movement to 3.05mm. Unlike the calibre 2003, calibre 2120 was fitted with not only a Gyromax balance, but also an anti-shock system. This made the movement rugged enough for use in a sports watch like the Royal Oak, and probably also explains why calibre 2120/2121 can even today still be found in the Jules Audemars Extra Thin and Royal Oak Extra Thin.


In 1986, Audemars Piguet went on to show that it could also make complications in ultra-slim fashion. With calibre 2870, the brand not only set a world record, but also introduced many firsts, most importantly being the very first automatic tourbillon! The watch was not fitted with a rotor that made a circular motion, but was equipped with a winding hammer crafted from a platinum-iridium alloy that powered the watch by horizontal motion.

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An ultra slim revolution: The first automatic tourbillon in the Audemars Piguet caliber 2870

Another first in this watch was the tourbillon cage that was crafted from titanium. Although quite a feature by itself, calibre 2870 also features the smallest tourbillon ever produced. With a diameter of 7.2mm it gave new meaning to the word understatement.

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The caseback doubles as the mainplate. Image by Walt Odets

The watch and movement are more or less the same for calibre 2870. To create such a thin movement, the overall height of the watch is only 5.5mm including the case. Here, the case functions as the main plate for the movement.

The same construction was recently deployed by Piaget to create the ultra-slim manual wind movement calibre 900P. Calibre 2870 went a bit more extreme however because the back of the case actually shows red synthetic rubies placed in it, indicating exactly where the gear train of the watch is located, everything to make the watch as slim as possible. For this reason as well, the crown was placed at the back of the watch.

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Audemars Piguet Royal Oak 1972-2012 Limited Edition

Enduring Statement

Today Audemars Piguet still serves watch enthusiasts with ultra-thin calibre 2120/2121. The fact that this movement is still used today, almost 50 years after its creation, clearly indicates the high quality of the original design in terms of reliability and durability. It’s no wonder that Audemars Piguet crafted a special skeleton version of this movement to power the Limited Edition(as shown above), because apart from the mythical design by Gerald Genta, this watch also owes a lot of its success to this movement.

[Adapted from an article by Martin Green in REVOLUTION’s archives.]

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