Once a watchmaker for the Italian navy, Panerai’s macho military style and in-house innovations have created a leading global brand. Timothy Barber reports.

Among its many merits, the recently opened Design Museum in London serves as a reminder of just how rarefied the category of “design classic” really is. Items such as Charles Eames’s lounge chair (1956), the Porsche 911 (1963), George Cawardine’s Anglepoise lamp (1932) or Harry Beck’s Tube map (1931) are not only formally satisfying, but have blueprints so strong that they’ve brooked little-to-no revision over the decades, without any loss of vitality and style.

As you may imagine, in watches there are a handful of examples – the Rolex Submariner dive watch, the Jaeger-LeCoultre Reverso, the Patek Philippe Calatrava, for instance. Few, however, have come to define the entirety of a brand through a single design – for that, one may turn to Officine Panerai, the Italian firm known exclusively for its large, cushion-shaped watches that have kept to the same essential template since 1936.

As a brand, Panerai is a fairly remarkable concoction: unearthed in the 1990s from almost total obscurity, it has spent 25 years essentially repeating itself, while imperceptibly growing into a luxury powerhouse. It has its own high-spec movement factory, a newly-announced sponsorship of the America’s Cup and a following of hardcore collectors – the self-proclaimed Paneristi – who are among the most obsessive in the luxury world. To that, it’s now adding a serious sense of innovation: this year it unveiled the Lab-ID, a watch with a space-aged movement the firm is guaranteeing for 50 years, meaning it should not need a service in that time.

It’s a remarkable development for a marque that existed for most of its life as a small-scale military tool. G Panerai and Figlio was a Florentine watchmaker and retailer (the brand still occupies the original shop opposite the Duomo), which in the 1930s won a contract to supply wristwatches and other precision diving instruments for use by frogmen in Mussolini’s navy. In particular, they were to be used by the divers who piloted the maiale human torpedoes that registered considerable success against Allied shipping in the Mediterranean.

In fact, these were the very first watches designed for professional military use under water. It was Rolex that supplied the distinctive cushion case and movement – in auction catalogues, vintage models are sometimes listed under Rolex rather than Panerai – while Panerai’s own design of dial was used. Conceived for strong legibility in darkness, its markings were cut out to reveal luminous paint, patented by Panerai itself, sandwiched underneath.

The arrangement continued after the war and, for several decades, Panerai remained a small and obscure affair. It was only in the 1990s that things came to greater attention when Sylvester Stallone discovered them in the window of the Florence boutique, commissioned a handful for friends and started wearing a Panerai on film. Soon, other watch aficionados – and the luxury conglomerate Richemont, owner of Cartier, Montblanc and others – caught up with an idea that a handful of collectors of the vintage military models had known for years: that Panerai had, pretty much by accident, created something seriously cool.

But a Panerai, compared with similarly chunksome “bro watches” from brands such as Hublot or IWC, has a cultured, old-fashioned allure that’s rather singular. My favourite is the Radiomir 1940 662 – with a brown dial that recalls the “tropical” patina found in some vintage examples. With the sparse, modernist dial language, great expanses of curving, polished surface, and straps of rich leather as thick as a horse’s bridle, Panerai watches are satisfyingly powerful, but deeply refined with it.

Richemont recognised this, and bought Panerai in 1997. Investment in a sizeable factory has brought a suite of its own movements, the sturdy style of which reflects the old utilitarian purpose with an emphasis on long power reserves and discrete complications. Last year, Panerai unveiled a minute repeater made entirely in-house. It’s an example of just how far a perfect design idea can be stretched, without actually being stretched very far at all. Perhaps only an Italian marque could come up with a utilitarian military tool that wears the sheen of luxury with such serendipitous style.

Timothy Barber is The Telegraph’s watch editor.