The present watch is one of the exceedingly rare examples of the so-called "drivers" reference 139; to the best of our knowledge only five other ref. 139 in white gold cases have appeared in public to date.
Reference 139, one of Patek Philippe’s earliest references, was launched in 1933, the “horizontal” pendant to references 137 and 138. It remained in production until around 1936 and was available in yellow and white gold. The name “drivers’ watch” is derived from its horizontal lay-out, allowing to wear it on the side of the wrist for easier reading of the time while driving.
Reference 139 is illustrated in Patek Philippe Wristwatches by Martin Huber & Alan Banbery, second edition, p. 118 & 119, pl. 156 & 165, a similar white gold example in Patek Philippe Museum - Patek Philippe Watches, Volume II, p. 212.