When Guido Panerai, grandson of brand founder Giovanni Panerai, secured a contract with the Italian Navy to provide luminescent equipment, Officine Panerai moved from being just a manufacturer of diving instruments to becoming one of the most influential watchmakers in the world. The company’s prized invention was a zinc sulphide and radium bromide concoction which they patented as 'Radiomir'. The radium, a radioactive substance that releases alpha and gamma rays as it decays, reacted with the zinc sulphide in such a way that made it glow. The company used its radium-based luminescent paint on various devices such as night-sights, compasses, depth gauges and calculators.

Guido’s son Giuseppe took over in 1934, shortly before the Navy requested that the brand make a robust diving watch that was as readable in low light as the company’s other instruments. As the watches were to be used underwater and at night by pilots of single-man submarines, the hands and markers needed to be much brighter than for use on land. The watchmaker provided two solutions to this problem—the first was to layer a dial that was completely covered with a thick coating of luminescent paint with a secondary dial that had slots cut from it, and the second was to hollow out channels from a dial in the shape of the markers, allowing thicker quantities of luminescent paint to be used. Both of these ideas had a satisfactory result, particularly at sizes that were unconventionally large for the time.

The engine that powered Panerai watches was a tried-and-tested Rolex movement, and was mounted in a steel oversized cushion case. Lugs were soldered to the case to allow fitment of a strap, making the watch wearable on the diver's wrist. Called the Radiomir after the radium that powered the luminescent paint, it was the birth of a design icon. It was tested in 1936 by the First Submarine Group, and was a resolute success.

Following the Second World War, the Radiomir evolved fixed lugs and the famous patented crown locking device. The Radiomir became the Marina Militare which, following the introduction of a less dangerous tritium-based radioactive luminescent material called 'Luminor,' became the Luminor. An enormous version built for the Egyptian Navy, the Egiziano, came in the 1950s, which later inspired the Submersible. A chronograph, the Mare Nostrum, stalled at the prototype stage.

There were no Panerai watches available for civilians until 1993, when the Luminor and the Mare Nostrum were released in limited runs. Their success attracted the interest of the Vendome Group, now the Richemont Group, which purchased the watchmaker. The distinctive and immediately recognisable style of the brand’s watches may have evolved for functional reasons, but that hasn't stopped Panerai from amassing a loyal following. It has proven that just because form follows function, it doesn't necessarily mean something can't look good too.