4100BA Audemars Piguet Royal Oak III

If you’ve ever been Royal Oak-curious, there’s never been a better time. Genta’s most brutal, industrial case design is as beautiful as it has ever been, but much less expensive that it has been historically. This is particularly true of the mid-sized case, and that even extends to precious metal. So technically, this is the pen of Jacqueline Dimier. Or maybe it was her photocopier set at 85%, I’m not sure. Either way, this is the 4100BA, the first mid-size Royal Oak to ever do 36mm. In fact, it was the third Royal Oak to ever exist after the 5402 and ‘Ladie’s’ 29mm ref. 8623. In AP archives, you’ll see it referred to as Royal Oak III. More true vintage than neo (you can tell by its 4-digit reference), it’s so Royal it even gets a III after its name.

Interestingly, Asia deemed the 5402 slightly too large for most wrists back then. 29mm didn’t meet the average standard either and so in 1977 this was made to tackle the problem. For those who like to see their calibres running, this is rather notably the first time the Royal Oak got a centre seconds. It was made from ’77-85, during which time 2721 were made in steel, 3563 in bimetal, and 2130 in this yellow gold. They are not rare, but they are lovely. The 4100 received its own calibre, the 2123, a JLC 900 ébauche just 3.25mm thin. And it was this very watch that kicked off a quite significant saga of wild complications and flamboyant dials which often debuted in the mid-sized case as a sort of testing ground for the jumbo.

To revisit the opening topic, in ’22 a lovely 4100BA hammered for 56K USD at Phillips. Cut 40% from that value, and that’s where they reside today. This is a market which has been more effected than most and for those who simply love the shape, which I find hard not to, it’s a miracle. This is particularly interesting as some of the latter mid-sized refs like 4332 and rarer 14790 dials (like Yves Klein, Salmon, etc) have held their values rather well. And a mid-size 3800J Nautilus is easily 75K. But the more obscure and widely produced 4100 is a relative bargain at the moment. Yes, it is definitely the lesser-known Luke Hemsworth to the 5402BA’s Chris. But Luke was surprisingly good in Westworld.


This example has very sharp case, with the pale gold dial (obviously, but here are many variations). Tritium looks all accounted for and great. The listing doesn’t note any extract, which might be worth pursuing. It comes from a well-regarded Belgian retailer.