The Audemars Piguet Royal Oak reference 5402ST, launched at Baselworld in 1972, is the original “Jumbo”. It has a 39 mm stainless steel case only about 7 mm thick, an octagonal bezel held by eight visible hexagonal screws, an integrated steel bracelet and a “tapisserie” dial with a fine square-grid pattern. Inside is the ultra-thin automatic calibre 2121, and the watch is water resistant to 50 metres. Gérald Genta reportedly drew the design in a single night.

It was radical for its time: a luxury watch in steel, priced above many gold dress watches, with a sports look that no Swiss house had tried. The first batches are known as the “A series” after the serial prefix, and details such as dial printing and lume shifted from series to series, which is why collectors speak of series and dial variations more than of the reference alone.

The 5402 is regarded as one of the most important watches of the twentieth century and created the luxury sports watch category that the Patek Philippe Nautilus and others later followed. Good A-series examples sell for very large sums at auction. The original 5402 is no longer made, but the Royal Oak line, including the modern extra-thin 39 mm Jumbo, remains Audemars Piguet’s core collection.