When American explorer Victor Vescovo made it to the bottom of the Mariana Trench last month, the record for the world's deepest manned submersible dive wasn't the only one to fall. His craft also had three Omega Seamaster Planet Ocean Ultra Deep Professional wrist watches strapped to the outside, and these specially made timepieces were subjected to a pressure of 1,085.10 ATM (15,946.5 psi) as they reached a depth of 10,928 m (35,853 ft), making them the deepest diving watches in history.

The dive watch holds a special place for enthusiasts, because the deep sea is the most difficult environment to protect against. Outer space, Mount Everest, Antarctica, the Sahara, and the powerful magnet fields of the Cern Supercollider all pose their challenges to the watchmaker's art, but it is at the bottom of the ocean that the ultimate foe is found.

Heat, cold, dust, shocks, and even magnetism are relatively easy for the designer to overcome, but water pressure that can squeeze a watch case apart or press the movement into immobility is the ultimate. Small wonder that the major Swiss watch companies have become so attached to diving, with their most advanced timepieces riding along on submersibles as they have plunged deeper and deeper into the ocean depths.

Perhaps the most famous example is from Rolex in 1960, when its specially made Deep Sea watch was installed on the outside of Jacques Piccard and Don Walsh's "Bathyscaphe Trieste" as it descended into the Challenger Deep in the Mariana Trench to reach a record dive depth for a manned craft of 10,916 m (35,800 ft).

Now Omega is claiming the crown of the deepest diving watch with its Seamaster Planet Ocean Ultra Deep Professional, which kept on functioning at a record depth of 10,928 m (35,853 ft) where it was was subjected to a pressure of 1,085.10 ATM (15,946.5 psi). Part of the Five Deeps Expedition, it was carried by Vescovo's DSV Limiting Factor – a titanium-hulled Triton submersible tended by the surface ship DSSV Pressure Drop as it dove in the five deepest regions of the world's oceans.

According to Omega, creating the Ultra Deep required a blank-sheet approach to the design. The idea was not only to produce a handful of watches for the record attempt, but also to have a design that would later be adapted to a commercial line of wrist watches. This meant that the Ultra Deep not only needed to be exceptionally strong, but also kept down to a practical thickness of under 28 mm.

To do this, Omega made the Ultra Deep watches out of scraps of grade 5 titanium plating left over from fabricating DSV Limiting Factor. Using advanced forging techniques and a weld-free design, these cast-offs were machined into the watch bezel, case, case back, and crown.

Meanwhile, the load-bearing surfaces of the thick sapphire crystal "viewport" were tooled to handle the pressure of the deep ocean and the cross section was tapered to minimize stresses. In between the sapphire and case was a layer of LiquidMetal – a commercial amorphous metal alloy developed by Caltech that has high tensile strength, corrosion resistance, very high coefficient of restitution, and high anti-wearing characteristics. This allowed the makers to dispense with a polymer seal and reduce the thickness of the crystal.

The end result is a forged titanium case rated to 15,000 m (49.212 ft) where the pressure is 1,489.06 ATM (21,883.1 psi) – well beyond that encountered by Limiting Factor.

The Ultra Deep design also boasts "manta" lugs that have been left open to reduce the risk of damage as the case deforms under pressure. These lugs secured the three Seamaster Planet Ocean Ultra Deep timepieces to the craft using polyamide straps and Velcro closures similar to those used on Omega watches supplied for NASA space missions. Two of the watches were installed on the submersible's arm and a third was strapped to a Lander – a small autonomous, recoverable sensor package used on the diving missions.

Omega says that the watches were pretested with a 25 percent safety margin. In addition, post-dive tests demonstrated the Ultra Deeps still met the standard of the Master Chronometer certification.

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