Blancpain Fifty Fathoms Automatique 45 mm 5015-1130-52A

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The storyWhy this reference matters

In 1952 captains Bob Maloubier and Claude Riffaud, who had just set up the French combat swimmer unit, tested the "waterproof" watches on the market and rejected the lot: too small, unreadable underwater and badly sealed. They heard that the head of a Swiss firm dived for his own pleasure in the south of France, and rang him. It was Jean-Jacques Fiechter, running Blancpain and a diver himself, who knew at first hand what fails down there. In 1953 he delivered a watch that met the specification in full.

What Fiechter put inside it is still the textbook for the genre: a unidirectional rotating bezel with a lock you had to press before turning; a crown with a double gasket; a case back designed so the O-ring would not twist as it screwed home; and a moisture indicator that turned from blue to red if water got in. The name comes from Shakespeare's The Tempest and works out at roughly 91.45 metres. The MIL-SPEC version, the pieces for the US Navy and the German Barakuda came later.

Quartz killed it: production stopped in the seventies and the Fifty Fathoms vanished. It came back in miniature with the 1997 Trilogy and at full size in 2007, as this reference 5015: 45 mm, a bezel with a sapphire insert and, above all, the calibre 1315. Three barrels in series give five days of running, with a free-sprung balance and a silicon hairspring — antimagnetic by design, not by shielding.

SpecificationsThe numbers, in one table

IdentificationHow to tell it apart

This is the Fifty Fathoms that keeps its engine hidden. The 5015-1130-52A has a solid steel back engraved with the brand name, "Fifty Fathoms" in script and the word ANTIMAGNETIC. Most variants in the 5015 family have sapphire backs, so if the photographs show you a window onto the calibre, you are looking at another reference however well the rest of the number matches.

Official measurements are 45 mm across by 15.50 tall, with 23 mm between the lugs. The dial is black with Arabic numerals at 12, 3, 6 and 9, applied luminous markers, a date at four thirty and the inscription "Fifty Fathoms 300 m / 1000 ft" above six. The bezel is unidirectional with a sapphire insert: the numbers and the luminous pip sit under the crystal, not printed on top of it.

Do not confuse it with the Bathyscaphe, the smaller, lower-profile sister line. This 5015 is the big one, the one on a sail-canvas strap with a rubber lining, with a pin buckle or a folding clasp to choose from. Inside, the automatic calibre 1315: 227 parts, 35 jewels, 4 Hz and 120 hours of reserve.

CollectingWhat collectors check

Try it on before anything else. Forty-five millimetres across by fifteen and a half tall is a lot of numbers in one place, and the canvas strap helps but works no miracles on a narrow wrist. It is the filter that rules out the most people and the one least often applied when buying online.

The sapphire bezel insert is brutally hard to scratch and yet it will chip if it takes a sharp knock on the edge. Go round the rim with a loupe looking for missing flakes, and turn it: it should click cleanly in one direction, with no dead spots and no lateral play. Replacing that insert is neither cheap nor quick.

The 1315 with its silicon hairspring is robust and shrugs off magnetic fields, but it is a three-barrel, five-day movement and an overhaul costs what it costs. With a solid back you cannot judge the movement's condition by eye, so service history counts for more here than usual. Check the canvas strap as well, which dries out with sun and salt, and ask for papers.

Common questionsWhat people ask us about this reference

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