The watch that launched the luxury sports watch category and kept Audemars Piguet afloat through thick and thin since 1972 was fittingly named after a 1916 Royal Navy battleship, the HMS Royal Oak. Without delving into its genesis and well-documented history, suffice it to say that the Audemars Piguet’s flagship Royal Oak has been interpreted in countless guises over the years. The Ref. 15500, a 41mm model of the RO with an upgraded in-house movement was introduced in 2019 and designed to replace the former Ref. 15400 that had been around since 2012. Offered with blue, grey and black dials, the latest iteration of Ref. 15000 now comes with a classic silver-toned dial. Combined with the steel case, the silver dial contributes to its solid monochrome look.The blue dial version of the Audemars Piguet Royal Oak Selfwinding 41mm 15500ST, introduced in 2019 – also with black and dark grey dials.Background Ref. 15500STLargely eclipsed by the launch of AP's polarising CODE 11.59 collection during the SIHH 2019, the presentation of the Royal Oak Selfwinding 41mm was actually big news. Replacing the former Ref. 15400, the 2019 Ref. 15500ST was upgraded with a new, larger, in-house movement and treated to several design tweaks. Collectors were pleased having complained that the movement inside Ref. 15400 (calibre 3120) was too small and meant that the date was marooned too far from the periphery for comfort. Although the CODE 11.59 collection was received with mixed reviews, the collection came with an entire line-up of new in-house movements, one of which was fitted inside the 2019 Ref. 15500. Ad - Scroll to continue with article In-house movement calibre 4302When it was introduced last year, the Ref. 15500 was equipped with the spanking new automatic calibre 4302 developed for the CODE 11.59 collection. Almost 6mm larger than its predecessor, the 32mm diameter of calibre 4302 is a more appropriate size for this 41mm model. The frequency was also increased to 4Hz (3Hz in past) and power reserve bumped up from 60 to 70 hours. Viewed from the caseback, the movement features a skeletonised gold rotor with the letters AP in the centre and sharp anglage along with Geneva stripes on the bridges and polished bevels.Silver-toned dialThe dial retains the signature guilloche Grand Tapisserie pattern everybody associates with the Royal Oak. Identical to the other dial colours in the Ref.15500 family, the little squares on the dial have more space between them and stand out more than in past editions while the minute track on the periphery of the dial is smooth with thin black markers printed against the white background. Enhancing legibility, the applied white gold hour markers are shorter and broader than the former reference and can carry more lume. Obviously the big change over Ref.15400 is the elimination of the hour marker at 3 o'clock to accommodate the date window, which is now tucked neatly against the minutes track. The date window has a white background and black numerals to echo the minutes track.41mm CaseThe stainless steel case measures 41mm and has a thickness of 10.4mm. All the signature traits of the RO are on display: the sharp, dynamic angles of the case; the iconic octagonal bezel with the eight hexagonal white gold screws; the integrated bracelet; and the beautifully brushed and polished finishes that highlight the architecture of the case. The crown is screwed-down and water-resistance rated at 50m.The Audemars Piguet Royal Oak Selfwinding 41mm in stainless steel (ref. 15500ST.OO.1220ST.04) retails for EUR 20,700?or USD 20,400. For more information, please visit audemarspiguet.com.