One of my all-time faves also happens to be one of Panerai’s all-time faves, which is a good thing because it re-emerges every few years in a “re-edition” with some new twist. Indeed, I stopped counting the number of times Panerai has reissued the Mare Nostrum, and hope that they never do because we love the periodic re-boots. That’s because it is a prime contender not just for “Coolest Chronograph Ever” but because it is also described by the brand itself, without any trace of hype, as the “most mysterious and rarest of all Panerai models”.

This is based on a simple fact: the original never actually reached production and was initially believed to exist only as a technical drawing. It was only in 2010 that the company discovered the original prototype and, to their surprise, it turned out to be much bigger than the mid-1990s, “pre-Richemont” reissue of 42mm. That first Mare Nostrum was 10mm larger, and it resulted in the PAM300 in a limited edition of 99 pieces, which sold out in a flash. Even a girth of 52mm didn’t deter buyers.

As watch stories go, it’s one of the most fascinating. When the Richemont Group (then named Vendôme) acquired the brand in the 1997, it was known only to military watch enthusiasts and Rolex collectors who knew the brand’s story intimately, for it is – in Rolex lore – merely a tiny footnote: Rolex’s involvement was in the early case design and manufacture, with Rolex-marked, Cortebert-based movements used to power certain models.

Geographically, the impact of the Mare Nostrum was even more focussed than the Dirty Dozen or the IWC Mk 11, both which were UK-centric with some issued throughout the Commonwealth. Panerais, also issued in tinier numbers than either of them, were exclusive to the Italian Navy, with some supplied to the Nazis in WWII, and even fewer to the Egyptian and Israeli navies in the 1950s, plus one or two other rumored naval forces.

When Panerai boss Dino Zei decided to revive the brand as a watch company in 1993, the re-launch was based on faithfully reimagined Luminors and Marinas. Then, to the delight of the cognoscenti, the company produced limited numbers of the near-mythical Mare Nostrum, based entirely on those original drawings.

Why the watch never appeared in the 1940s, when it was conceived, was due to wartime conditions. The Mare Nostrum was commissioned as the company’s first-ever chronograph, probably for deck officers, but events – not least Italy’s surrender – probably resulted in its still-birth. The resultant reissue was, instead, a 42mm realisation of the drawings found in the few archives that survived the devastating 1966 flood in Florence.

It was given the identification of Ref. 5218-301/A. Inside was a manually wound ETA 2801 movement and Dubois-Depraz module, while the distinctive dial bore two sub-dials and the hefty case featured two pushers. For me, actual production numbers of pre-Richemont Panerais seem to have the fluidity of the sea itself, and Paneristi, known for their near-psychotic pedantry and typical inter-collector rivalry, argue it to this day, but there is reason to believe that the pre-Richemont Mare Nostrum achieved production of less than 500 examples of all the variants.

Given the freedom afforded by working from drawings-only, as opposed to the models reissued after the re-discovery of a prototype, Panerai was able to issue the first-generation Mare Nostrums with dark blue, black or white dials, at least two bezel styles – engraved and smooth – are known, and the ones that cause collectors to swoon are the Sylvester Stallone-associated models with Slytech identification on dial and caseback. The standard, most common first-gen Mare Nostrum, though, had the dark blue dial and engraved tachymeter bezel marked in kilometers.

Values of the pre-Richemont Mare Nostrum today ebb and flow, as do those of the various 21st century reissues. Mine was acquired in 1997 in Milan for a then-terrifying £900. One of the wisest watch purchases I ever made….