Diving into the Fifty Fathoms legend

on November 2, 2025

1 minute read

From accident to icon: in the 1950s, an underwater scare prompted Jean-Jacques Fiechter to create the Fifty Fathoms, the first true modern diving watch.

It all begins with a potentially fatal accident. In the 1950s, Jean-Jacques Fiechter, head of Blancpain and passionate diver, loses track of time underwater... This marks a turning point. Jean-Jacques Fiechter begins to reflect on the limitations of watches at the time: uncertain water resistance, poor readability, vulnerable mechanisms. He wants to go further. His goal: to design the first truly reliable diving watch. Three patents would give birth to the Fifty Fathoms — not a beautiful object to show off on land, but a tool designed to survive the depths.

Three Key Patents

Double-sealed crown (non-screw-down)

The first seal prevents water from entering during handling, while a second, located inside, provides extra security in case of accidental pulling underwater.

Rotating bezel with locking mechanism

Fiechter envisioned a dive bezel that rotates in only one direction to prevent any measurement errors. He filed a patent for a locking mechanism that requires pressure to be applied before rotation.

Enhanced screw-down case back

A third patent was granted to Fiechter for his reinforced groove system, where the O-ring is held in place by a metal disc. This prevents twisting or misalignment when closing the case back.

To these three patents, Fiechter added visionary choices: automatic winding, large diameter, high black-and-white contrast, luminescent markers, and even anti-magnetic protection with an internal soft iron cage — anticipating the electromagnetic disturbances encountered during diving.

©Blancpain

A Shakespearean Name

Fifty Fathoms refers to a passage from Shakespeare’s *The Tempest*: “Full fathom five thy father lies; of his bones are coral made.” *Fifty* (rather than *five*) evokes deep-sea diving, referring to a water resistance of 50 fathoms — or 91.45 meters.

Bob Maloubier and Claude Riffaud, founders of the French combat divers unit, were looking for a watch that met the specific needs of underwater missions. Fiechter’s prototype ticked all the boxes: water-resistant, legible, and robust. The Fifty Fathoms became the standard-issue instrument for the French Navy, and later for other armed forces.

But an administrative obstacle arose: France required military equipment to be purchased from domestic companies. Blancpain then partnered with Spirotechnique (part of the Air Liquide group), distributing the watches under the “Aqualung” brand. This partnership created a strong connection with Jacques-Yves Cousteau — as Air Liquide belonged to his wife's family. The Commander chose the Fifty Fathoms for his team during the filming of The Silent World.

©Blancpain

No Radiations

This inscription, found on the dial of a 1950s version of the Fifty Fathoms, indicated that the luminescence was achieved using non-radioactive tritium — including on military models — rather than radioactive radium.

©Blancpain

Milspec 1 and 2

In the United States, the Fifty Fathoms became a military watch thanks to Allen Tornek, who established a local lab to bypass import restrictions. The US Navy adopted the Milspec 1 in 1957, featuring a moisture indicator disc, with 611 units produced. Even rarer, the Milspec 2 TR-900—anti-magnetic and sandblasted—was produced in only 1,080 units between 1964 and 1966.

Birth and rebirth of the Fifty Fathoms

©Blancpain

1953

Creation of the Fifty Fathoms by Jean-Jacques Fiechter, CEO of Blancpain and diver, featuring a double-sealed crown, a rotating bezel with locking mechanism, and an improved screw-down case back.

©Blancpain

2003

Rebirth of the Fifty Fathoms with the Fifty Fathoms Anniversary, a limited edition of 50 pieces, under the leadership of Marc A. Hayek, current President & CEO of Blancpain and passionate diver.

©Blancpain

2007

New launch of the Fifty Fathoms collection, which has since become one of Blancpain’s cornerstones.

38 mm

The diameter of the Bathyscaphe for women (2013) and a new version of the Fifty Fathoms Automatique, launched in 2025 and equipped with the Blancpain Manufacture Caliber 1150. The new 2025 timepieces are also available with the Caliber 1153 (no date), depending on the model. Just like the Bathyscaphe, the Fifty Fathoms family is now complete with sizes suited to every wrist.

40 mm

Originally, the Fifty Fathoms had a diameter between 40 and 41 mm — considered large at the time — but necessary to make it a reliable diving instrument.

42 mm

In 2024, Blancpain introduced 42 mm versions, a smaller alternative to the 45 mm model while maintaining the Fifty Fathoms aesthetic.

43 mm

In 2013, Blancpain relaunched the Fifty Fathoms Bathyscaphe, 43 mm (originally created in 1956).

45 mm

The standard size of the Fifty Fathoms, used for many automatic models and other variants, such as the limited edition Blancpain Ocean Commitment of 2025.

47 mm

In 2023, the launch of the Fifty Fathoms 70th Anniversary Act 2 – Tech Gombessa, a new line with a 47 mm diameter.

55.65 mm

The X-Fathoms model, launched in 2012, is a technical version of the Fifty Fathoms, equipped with a mechanical depth gauge.