Breguet Type XX Case number 1669 with a red tachymeter scale.
Confirmed by Breguet. Hyper rare configuration. This is the first time I see it. I start to realize that these vintage Breguet Type 20 are a kind of Pandora box, with a strong diversity of versions... A bit like these good old vintage Blancpain Fifty Fath...
Gorgeous.
The last issue of "Le Quai de l'Horloge" has a couple of very nice articles about the history of the Type XX / Type 20 (I didn't even know that both are correct and that refer to different watches) and of the modern era Type XX.