Introduced to the market in 1958, the same year as Patek Philippe’s calibre 12-400, reference 3418 represents one of the manufacture’s most unconventional stainless-steel wristwatches of the period. Its defining feature is the ingenious patented “convertible” case construction, designed to allow the watch to be changed between a leather strap and a metal bracelet through a system of interchangeable attachment components secured by a threaded retaining ring on the case back. The present example is powered by the manually wound calibre 12-400 and is fitted with a stainless-steel Milanese bracelet.

Known among collectors as the “Convertible”, reference 3418 was produced exclusively in stainless steel and is distinguished by its ingenious modular case construction, which allowed the watch to be configured either with a metal bracelet or with separate lugs for a leather strap. The present example is powered by the manually wound calibre 12-400 and retains its characteristic stainless-steel Milanese bracelet supplied by Cornu & Cie of La Chaux-de-Fonds, with the clasp bearing the “UNROC” signature — Cornu spelled backwards. The separate lug components for use with a leather strap do not accompany the present example.

Another particularly interesting feature is the construction of the dial. Rather than conventional applied or printed baton indexes, the hour markers are engraved directly into the dial, creating the visual impression of applied markers.

The present watch, movement no. 728'263 and case no. 2'605'908, appears to belong to the earliest production of the reference. A closely related example sold by Phillips, with case no. 2'605'905 — only three numbers apart — and movement no. 728'423, was confirmed by its Patek Philippe Extract from the Archives as having been manufactured in 1958 and subsequently sold on 30 September 1959. Another example sold by Christie’s, movement no. 728'325 and case no. 2'605'856, was confirmed by its Extract as having been manufactured in 1957 and sold on 10 June 1959. The remarkably close correspondence between these case and movement numbers strongly suggests that the present watch belongs to the earliest group of reference 3418 watches.

Combining an ingenious convertible case, unusual dial construction and distinctive Milanese bracelet, reference 3418 stands apart from Patek Philippe’s more traditional dress watches of the period and represents a particularly technical and experimental chapter in the manufacture’s post-war production.