The tank simulates pressure at 16,000ft below sea level and it is inside that Rolex's Deepsea watches are tested before release onto the market.
It is, potentially, an expensive process. The smallest flaw in each watch's construction will make it explode, so it pays to make sure everything is right before undergoing this hyperbaric assault.
But this also means that the company has, for decades, been able to supply specialist pieces for divers working for the likes of Comex, the underwater engineering firm whose elite members hold the world record for the deepest saturation dives.
Rolex can also claim credibility for the wearer whose depths rarely surpass that of his morning shower. In fact, each Rolex is tested to a depth 25% greater than that stated on the dial.
And that's by no means the only test a watch might go through. Rolex, for instance, puts its Oysterlock bracelets through 26 different kinds of drop tests; the fastening is opened and closed tens of thousands of times; it's immersed in salt and sandy water and in chlorine solutions.
Taking testing to the extreme
"Shock, acidity, temperature, magnetism, legibility... all the variables that might affect a watch's performance have to be tested for," says Jean-Paul Girardin, vice president of Breitling. "These tests have to comply with regulations local and global, because our customers travel."
"The more extreme the conditions a watch has to operate in, the more extreme testing has to be. We tested our Emergency watch to minus 20 degrees Celsius (minus four degress Fahrenheit), for example - that would freeze the oils in any normal watch. There was no test at all for the transmitter batteries we developed for the same piece, so you end up establishing your own standard. You need a lot of skills outside of watchmaking: mathematicians, physicists, chemists..."
Life is crude
And, occasionally, a big steel hammer to hit your watch with, over and over. Dubbed the 'sheep's foot test' by those in the business, this is one of the oldest but still most important of trials for many Swiss timepieces.
"It's a very crude test. People think you're kidding when they see it: 'what, you're going to whack that very expensive watch?'," says Theodore Diehl, horologist for Richard Mille. "But it's no less important for being crude. Life is crude, after all. You drop your watch on a concrete floor and the result isn't subtle."
With a watch predicated on the very idea of toughness, Casio's G-Shock similarly goes through a barrage of tests.
Prototypes underwent a rather rudimentary trial by height when their designers dropped them from ever taller heights of the Japanese brand's R&D building.
Indeed, such has become the fame of the watch's robustness that there is a YouTube subculture featuring amateur tests of owners' own invention, among them shooting at the watch and driving over it in a Hummer.
Going above and beyond
Certainly the shift to ever higher performance means that watches increasingly surpass the tests they must go through to meet COSC certification as a chronometer. COSC, the Controle Officiel Suisse des Chronometres
, is the body responsible for the accuracy and precision of Swiss watches.
Omega, for instance, had to work with the young Swiss-government METAS agency to certificate its Master Co-axial movement because their precision standards were that much higher.
Wear and tear
Yet while watchmakers get very technical in their testing, sometimes old-fashioned wear trials are just as important to find out how a watch performs when it's actually being worn.
If Rolex does this through automation -- a robot arm mimics everyday movements, as well as those of certain sports or activities, to simulate a year of wear in a week -- Breitling actually sends prototypes out to, Girardin says, "people in the field - pilots, gardeners, sportspeople, office workers" to get their personal feedback.
Do tests translate to sales?
But do customers themselves care that their watch has been through such punishing regimes? Rob Wilson, international marketing manager for Seiko, says they do.
Certainly strapping a watch to the side of a submarine may smack of having an eye more on promotion than performance, he argues, but being able to prove a watch's capabilities can both justify prices and undoubtedly appeals to the nerdier, typically male consumer.
"We even include the test results of our Grand Seiko watches in with each watch, which underlines the standards used but also the individuality of that watch's particular performance," says Wilson. "And that certificate matters. Keep hold of it and the value of that Grand Seiko to collectors will be considerably higher than one without it."
All video in this piece provided by Casio G-Shock