Engineered to Challenge the Deepest of Seas Some watchmakers like to go out on a limb. Rolex is one of them. When the submersible Deepsea Challenger carried the film director and explorer James Cameron this year on the first solo trip to Challenger Deep in the Mariana Trench in the Pacific Ocean, the deepest known place on the planet, it also carried the Oyster Perpetual Rolex Deepsea Challenge, an experimental divers" watch developed and manufactured for the occasion, attached to its external manipulator arm. Mr. Cameron's solo record dive of nearly 11,000 meters, or about 36,000 feet, echoed a historic 1960 dive to 10,916 meters by the Swiss oceanographer Jacques Piccard and Lt. Don Walsh of the U.S. Navy. On that dive, an Oyster Deep Sea Special was attached to the hull of their bathyscaphe, the Trieste. In both cases, the watch remained in perfect working order when it returned to the surface. Technically, the Rolex Deepsea Challenge is an enhanced version of the commercial Deepsea professional divers" watch introduced in 2008 and guaranteed to be waterproof to a depth of 3,900 meters, thanks to a case architecture incorporating a patented ringlock system. The system features a case back 5.3 millimeters, or 0.2 inch, thick in highly resistant Grade 5 titanium and a near-indestructible nitrogen-alloy stainless steel support ring that provides reinforcement to a dome-shaped sapphire crystal in high-purity aluminum oxide, 5 millimeters thick, protecting the face. The new watch, however, is guaranteed to be waterproof to a depth of 12,000 meters, helped by a thickening of the sapphire crystal to 14.3 millimeters. To comply with the stringent certification requirements for divers" watches, the watch was tested in a specially created hyperbaric tank at a pressure of 1,500 bars, corresponding to the water pressure at a depth of 15,000 meters. Diver's watches have long been an effective marketing tool for watch brands to demonstrate their technical prowess. "At the start of the last century, the water resistance of a watch was a proof of quality, because the dust could not get inside either," said Thomas Houlon, director for diversification and innovation at Tag Heuer. Such a watch was not only more precise, but would last much longer. "Then it became an exercise in difficult watchmaking, to be as thin as possible with maximum water resistance," he said. Designing to such limits goes beyond the practical needs of most wearers, Mr. Houlon conceded. "It's true that you don't dive at 200 meters every day," he said, "but in the end it's like a tourbillon, or a chronograph with a precision of one-thousandth of a second: You don't measure to 1,000 per second, but when you have such a watch, it's so exceptional, so complicated to build, that it makes its value. So it's not about prestige, it's about the performance of the making of such an instrument. The Baselworld watch fair in March included many new or revised iconic diving watches, and several brands looked at their heritage collections from the 1950s through the 1970s for design inspiration. Rolex updated its no-date Submariner, first introduced in 1953, with a slightly redesigned case (but still 40 millimeters), a new ceramic bezel in cerachrom, a solid-link bracelet in steel with Oysterlock safety clasp and Rolex's patented glidelock extension system. Meanwhile, Rolex's sister brand, Tudor, released the Black Bay diver, whose design is inspired by the Tudor Submariners of the 1960s and 1970s, with a "chocolate" dial with gilt lettering, high-domed crystal, oversize crown, snowflake hands (from the first Snowflake Submariner in 1967) and an aluminum bezel in matte burgundy that gives it a vintage look. The 41 millimeter-diameter watch is only 10 millimeters thick and has a water resistance of 200 meters.