AUDEMARS PIGUET Audemars Piguet, « Ra Tourbillon Automatique », Ref. 25643BA case no. 231, made in 1987 and sold in 1988 An extremely fine and rare, collectible, extra-thin, automatic, oval shaped, 18K yellow gold wristwatch with visible one-minute tourbillon regulator and oscillating weigth, champagne dial with sunray pattern, applied gold dot indexes, black oxidized Feuille hands, leather strap and an 18K yellow gold Audemars Piguet double deployant clasp. Fitted with a Cal. 2870, extra thin, hand engraved, 32 jewels, lateral lever escapement with visible one-minute tourbillon regulator with titanium cage, monometallic balance with timing screws, self-compensating flat balance spring, self-winding with visible swinging weight, monobloc gold case set with jewels on the back, snap on gold bezel, back winder, sapphire crystal. Glass, rotor, case and movement signed, case and movement numbered. Dim. 28.60 x 32.80 mm. Thickness 5.40 mm. Approx. overall length 185 mm. Audemars Piguet has always inspired enthusiasm and surprise with its one-of-a-kind creations. The 1986 “Tourbillon Automatique” model is one such example; not only is it the world’s first wristwatch equipped with a self-winding tourbillon, but it is also the thinnest and smallest, with a tourbillon whose height does not exceed 4.8 mm, thanks to its case, which also serves as the movement’s main plate (a design inspired by Delirium Tremens watches), and it is also the lightest, weighing just 0.134 grams. The traditional circular rotor is replaced by a pendulum-style oscillating weight made of a platinum-iridium alloy, (a design reminiscent of the first Breguet perpetual watches); the winding and setting crown is positioned beneath the case, and for the first time, an ultra-lightweight and rigid titanium cage has also been created. The Caliber 2870 is housed in an ultra-thin case measuring just 5.3 mm in thickness. The Caliber 2870 that powers the watch traces its origins to the P-29 project, developed by André Beyner and Maurice Grimm and patented on October 24, 1980, under patent no. CH643701. This project, rejected by Ebauches SA, aimed to create an ultra-thin watch with a self-winding movement to counter the rise of ultra-thin quartz watches. The two engineers subsequently left Ebauches SA and used this ultra-thin automatic movement concept to create an ultra-thin tourbillon watch. Only a few prototypes of this first ultra-thin automatic tourbillon were built before the search began for a manufacturer interested in marketing such a watch. Prototype No. II went on sale at Phillips in November 2025. Audemars Piguet expressed interest in this new concept and, at the 1986 Basel Fair, launched its “Ra” model, of which approximately 350 pieces were sold over the next two decades. Compared to the original prototypes, it is worth noting that AP chose to change the orientation of the movement so that the tourbillon cage is positioned at the top left near the 12 o’clock mark, and that the case back now serves as the movement’s main plate, replacing the classic screw-down case back. The model was named « Ra », Ra being the supreme Sun God and King of the Gods in ancient Egyptian mythology, a reference to the dial layout, where the visible tourbillon cage shines like the sun, with the guilloché pattern on the dial serving as its rays. As a true technological demonstration of all the expertise of Audemars Piguet, known as “The Master of Complications,” this watch continues to captivate enthusiasts. The model is described and illustrated in Audemars Piguet 125 ans d’audace, by Gisbert L.Brunner, Christian Pfeiffer-Belli, Martin K. Wehrli, edition 2000, pages 274 & 275. PLEASE NOTE that the present watch is not in working condition and require a full-service at AP manufactory. However, the case and dial are extremely well-preserved with very few signs of wear.