Original vintage 1960s Rolex ad for the company's specially designed dive watch - the Rolex Deep Sea Special - for the bathyscaph Trieste mission.  "Six miles down...six tons pressure per square inch...a Rolex Oyster on the OUTSIDE of the bathyscaph 'Triete'!"
 
Dimensions: Roughly 10.25 inches wide by 13.5 inches high.
 
The Philippine Sea was rough on the morning of 23 January 1960, which made launching the U.S. Navy bathyscaphe Trieste into the abyss a challenge.
 
"But once it was under way, the deepest dive in human history was actually a little boring," notes Don Walsh, the 28-year-old Navy lieutenant who piloted the Trieste together with Swiss oceanographer Jacques Piccard on its nine-hour plunge to the deepest point on Earth – a 10,916 meters (35,800 foot) depression called the Challenger Deep, some 320 kilometers (200 miles) southwest of Guam in the Mariana Trench.  Although, Walsh adds, that boredom was interrupted by "one moment of pure terror."
 
They were two-thirds of the way to the bottom when a crash rocked the hull of the small, free-diving bathyscaphe. Walsh and Piccard shot each other a glance, and braced themselves for the end. And then – nothing happened. “It was just that one crash, like an explosion, and then nothing,” says Walsh.
 
They later learned that a Plexiglas exterior window had cracked from the pressure, which they measured at one ton per square centimeter, nearly 1,000 times that at the surface. The cracked window “wasn’t life-threatening, at least not immediately”, Walsh says with a shrug.
 
The bathyscaphe Trieste was a pioneering research vessel that achieved the first manned descent to the deepest point in the ocean, Challenger Deep in the Mariana Trench – the deepest point in Earth’s seabed – in 1960. Designed by Swiss physicist Auguste Piccard and acquired by the U.S. Navy in 1958, the Trieste made its historic dive on January 23, 1960, with Jacques Piccard and Don Walsh on board, reaching a depth of approximately 35,000 feet.
 
The mission was the final goal for Project Nekton, a series of dives conducted by the U.S. Navy in the Pacific Ocean near Guam.  Trieste consisted of a heavy crew sphere suspended from a hull containing tanks filled with gasoline for buoyancy, ballast hoppers filled with iron shot and floodable water tanks to sink.
 
The pressure sphere was attached to the underside of the hull and accommodated two crew who accessed it via a vertical shaft through the hull; this access shaft was not pressurized and flooded with seawater on descent.  The sphere was completely self-contained, having a closed-circt rebreather system with oxygen provided from cylinders while carbon dioxide was scrubbed from the air by being passed through canisters of soda-lime, and batteries provided electrical power.
 
The buoyancy tanks were filled with gasoline, which floats in water and is similarly incompressible.  Changes in the volume of the gasoline caused by any slight compression or temperature changes were accommodated by the free flow of seawater into and out of the bottom of the tanks during a dive via valves, equalizing the pressure and allowing them to be lightly built.

Following its acquisition by the United States Navy, Trieste was modified extensively by the Naval Electronics Laboratory, San Diego, California, tested in the Pacific Ocean over the next few years, and culminated in a dive to the bottom of Challenger Deep in late January 1960.  Before this, the Trieste departed San Diego on in early October 1959 for Guam aboard the freighter Santa Maria to participate in Project Nekton, a series of very deep dives in the Mariana Trench.
 
On January 23, 1960, it reached the ocean floor in the Challenger Deep (the deepest southern part of the Mariana Trench), carrying Jacques Piccard and Don Walsh. This was the first time a vessel, crewed or uncrewed, had reached the deepest known point of the Earth's oceans.  The onboard systems indicated a depth of 11,521 meters (37,799 ft), although this was revised later to 10,916 meters (35,814 ft); fairly recently, more accurate measurements have found Challenger Deep to be between 10,911 meters (35,797 ft) and 10,994 meters (36,070 ft) deep.
 
The descent to the ocean floor took 4 hours 47 minutes at a descent rate of 0.9 metres per second (3.2 km/h; 2.0 mph). After passing 9,000 meters (30,000 ft), one of the outer Plexiglas window panes cracked (as noted above), shaking the entire vessel. The two men spent twenty minutes on the ocean floor.
 
The temperature in the cabin was 7 °C (45 °F) at the time - while at maximum depth, Piccard and Walsh unexpectedly regained the ability to communicate with the support ship, USS Wandank (ATA-204), using a sonar/hydrophone voice communications system. At a speed of almost 1.6 km/s (1 mi/s) – about five times the speed of sound in air – it took about seven seconds for a voice message to travel from the craft to the support ship and another seven seconds for answers to return.
 
The dive of the Trieste was more than a record-setting voyage. With it, Piccard and Walsh opened a scientific window on the deepest ocean, which until then was widely considered devoid of life. Touching down on the bottom, the pair used mercury vapor lamps to survey their pitch-black surroundings – and were taken aback by what they saw.  “By far the most interesting find was the flatfish we could see through the porthole lurking on the ocean bed,” Piccard later said. “We were astounded to find higher marine life forms down there at all.”

“Today scientists are continuing to study a remarkably complex ecosystem in the abyssal depths of the sea, built upon hundreds of species of foraminifera – single-celled, “shelly” organisms that make up more than half of all living matter and comprise the lowest link of the oceanic food chain. In the ooze of the Challenger Deep, scientists found more than 400 species, whose DNA resembles some of the earliest life forms on Earth.
 
The Trieste was returned to San Diego and taken out of service in 1966. Between 1964 and 1966, Trieste was used to develop its replacement, the Trieste II, with the original Terni pressure sphere reincorporated in its successor.  In early 1980, it was transported to the Washington Navy Yard where it remains on exhibit today in the National Museum of the U.S. Navy, along with the Krupp pressure sphere.
 
The Watch
The Rolex Deep Sea Special that went down on the deepest dive was found to be in perfect working order after its legendary expedition to 10,916 meters.  To demonstrate the extraordinary efficiency of the watch, Rolex started collaborating with Auguste Piccard, and the Trieste had already dived several times in previous years with earlier versions of the Deep Sea Special affixed to its hull, reaching 1,080, 3,150, 3,700 and finally 7,300 meters before the ultimate challenge was taken up.
 
The Rolex Deep Sea Special strapped to the exterior of the Trieste was unfazed. “Happy to announce that your watch works as well at 11,000 meters as it does on the surface,” Piccard later telegraphed to Rolex headquarters in Geneva.
 
The Deep Sea Special was technically identical to the Oyster, but enhanced with larger features, such as a wider surface of watch glass, allowing it to withstand underwater pressure. The advertisement available here underlines the waterproof qualities of the Oyster.