Launched in 1972 at Basel Fair, Audemars Piguet's introduction of the Royal Oak marked the beginning of the luxury sports watch market we know today, causing an immediate sensation as the watch industry had never seen anything comparable before. At the time the most expensive stainless steel wristwatch available, it most notably housed the extra slim calibre 2121 based on the Jaeger-LeCoultre cal. 920, that would later be found in the Nautilus wristwatch.