A JLC 920 with a Vacheron name
The Cal. 1120 is Vacheron Constantin's rebranded version of the Jaeger-LeCoultre Cal. 920, designed in 1967 as the world's thinnest full-rotor automatic. JLC sold the 920 only to other manufactures: AP (as Cal. 2121), Patek (as Cal. 28-255), and Vacheron Constantin (as Cal. 1120). The three companies then finished and decorated the same base movement to their own house standards.
In the Vacheron 222
In 1977 Vacheron Constantin used the 1120 in the ref. 222, the brand's answer to the Royal Oak and Nautilus and the third "luxury sports watch with integrated bracelet" of the Genta era (although the 222 was designed by Jörg Hysek, not Genta). The 222 case was 37 mm and very thin, made possible by the 1120's 2.45 mm height. The 222 is now considered the spiritual ancestor of the modern Overseas and was reissued as the Historiques 222 in yellow gold (2022) using a modern descendant of the 1120 architecture (the in-house Cal. 2455/2).
In the original Overseas
When Vacheron launched the Overseas in 1996 (ref. 42042) as a successor concept to the 222 and the Phidias, the engine was again the Cal. 1120. The Overseas Generation 1 (1996-2004) used the 1120; Generation 2 (2004-2016) moved to the Cal. 1226 / 5100 family; Generation 3 (2016+) uses the in-house Cal. 5100/5200 with 60 h reserve. The 1120 also powered the Patrimony Contemporaine ultra-thin and various dress watches in the 1980s-2000s.
The end of the JLC base era
JLC ended production of the Cal. 920 family in the 2000s; existing stock at AP, Vacheron, and Patek lasted into the 2010s. Vacheron's in-house replacement, the Cal. 5100 / 5200 family, brought 60 h reserve and modern hairspring technology while keeping the slim profile. The 1120 itself remains in service: AP and Vacheron stocked enough movements to support the back catalogue, and parts are obtainable through both manufactures' service networks. Watches running the 1120 are now considered "vintage modern" and are sought by collectors who want the Genta-era aesthetic with the original engine.
Why the JLC-base trio matters
The 1120 (Vacheron), 2121 (AP), and Patek 28-255 family share the same DNA. For collectors this is one of the most fascinating overlaps in horology: three of the four "Holy Trinity" maisons all building their flagship sport watches on the same JLC base for fifty years, with each adding its own finishing, rotor design, and brand signature. Identifying which of the three you are looking at is a matter of rotor shape, plate decoration, and signature engraving rather than architecture.
