The waves are starting to kick up as the Molly V approaches the mooring buoys marking the wreck site. Captain Jitka throttles back the engine and I clamber to the bow to tie us in. A mile behind us, I can see the towers of the Mackinac Bridge set against the steely sky and I wonder how many of the thousands of drivers who cross it between Michigan’s peninsulas know of the carnage just beneath the water’s surface.

The Mackinac Straits hold a half-dozen significant shipwrecks, like the Eber Ward, the Minneapolis and the Sandusky, but there is one I’ve dreamed of diving more than any other ever since I heard of it 10 years earlier – the Cedarville. And now it is 75 feet below us, a massive presence whose only evidence at the surface are the three widely-spaced buoys marking the bow, amidships and stern. Though the depth here isn’t extreme, conditions can be tricky; the narrow Straits funnel water from Lake Michigan into Huron and currents can make for dangerous diving. I double check my equipment – drysuit valves, regulators, weights – and snap shut the clasp on my Rolex Sea-Dweller 4000, spin the timing bezel to zero, then shuffle to the transom and plunge into the 45°F (7.2°C) water.

Everything about the Cedarville is superlative. At 600 feet long, it is the third longest wreck in the Great Lakes. The doomed ship’s final resting position is dramatic, twisted around its torn middle so that the bow is upside down, seemingly supported by its spindly radar mast, which is dug into the lakebed. Our dive boat is moored to the bowline and as I descend, the ship’s upturned hull comes into view mere feet below the surface, magnetically drawing me deeper. At 35 feet, I pass the top of the wreck until I am in its shadow and then, at 75 feet, my feet touch down on the lunar surface with a puff of silt.

Under Pressure

By the mid-1960s, diving was no longer merely for recreation or military purposes. The discovery of offshore oil reserves spurred an oceanic gold rush to harvest the millions of barrels below the seafloor. Deepsea divers were in high demand for work that little resembled the reef-combing of vacation scuba. Their work involved laying, welding and maintaining drilling equipment and pipelines on the bottom of the sea. The job was difficult and the hours breathing compressed gas required that the divers live for days at a time in a pressurised chamber underwater.

The divers would alternate between time working in the water and downtime inside the dry chamber, which was pressurised the same as the water in which they were working. The breathing gas in the chamber was made up predominantly of helium with a minimal amount of oxygen. This allowed them to work at great depths without experiencing the narcotic effects caused by breathing pressurised air. The gas affected the divers’ voices, making them sound like chipmunks, but it also had an effect on their wristwatches.

Helium atoms are tiny and during the time inside the dry chamber, the high-pressure gas would seep into their watches, past the rubber seals. At the end of their days at depth, the chamber would be slowly depressurised to bring the divers safely to surface air pressure. As this happened, the helium atoms inside the watch expanded, until the pressure increased, blowing off the crystal, often ruining the watch. COMEX, a pioneer of commercial diving and undersea exploration, approached Rolex for a solution. You can read that story here. The short version of the story is that eventually it lead to the birth of the Sea-Dweller in 1967 — or exactly 50 years ago.

Two years earlier, in May of 1965, the SS Cedarville was steaming through the Mackinac Straits with a full load of limestone. There was heavy fog and by the time the Norwegian freighter, Topdalsfjord, came into view it was too late. The ships collided, causing a gash in the Cedarville’s hull below the waterline. While the ship filled with water, her crew tried to steer her for the shoreline but it was in vain, and she capsized and sank, taking with her 10 of the 35 crew members. A half a century later now, the fresh, cold waters have preserved the wreck remarkably, and I tentatively swam aft from beneath the upside down pilothouse to try to find the ship’s fatal wound. The glowing blue minute hand of the Sea-Dweller reassuringly indicated I had only been down for 12 minutes and at this depth, I could safely stay for 40 more.

Safety Valve

The first Sea-Dweller evolved from Rolex’s Submariner, which was already capable in its own right, one of the first dive watches and one favoured by divers, professional, military, and amateur alike. To withstand the greater depths common in commercial diving, Rolex beefed up the Submariner’s case and crystal. Eventually, a longer dive suit extension was added to the clasp for wear over the thick exposure suits needed for an eight-hour shift at the bottom of the North Sea. But what set the Sea-Dweller apart was what Rolex added to the watch’s left flank – a gas release valve. This small one-way plug would pop out if pressure inside the watch got too high, allowing trapped helium to harmlessly vent to the atmosphere. This patented innovation worked well and the Sea-Dweller was quickly adopted as the watch of choice by commercial divers working in pressurised habitats.

In the history of wristwatches, there is no better example of a “tool watch” created for such a specific purpose and audience than the Rolex Sea-Dweller. A helium release valve is useful to a tiny handful of people who find themselves living in a pressurised environment where helium could wreak havoc on less-evolved timepieces. So narrow was the Sea-Dweller’s target audience that it was a full two years after its introduction that Rolex even decided to sell it publicly. After all, why would watch buyers, even diving ones, bother to spend more for something they would never use to its full capabilities? Fast forward to today and countless dive watches from many brands sport helium release valves, sold to unwitting buyers who won’t settle for anything else even if they don’t know its purpose. Along the way, the Sea-Dweller became an icon.

Swimming back against a current for what seems like an age, I finally come across the great gash in the Cedarville’s flank. Here the hull is lying on its starboard side and its cargo of limestone has spilled out into a massive debris field on the lake bottom. Daylight streams through the gap between the halves of the ship, evidence of the great trauma of its collision and sinking. I ascend slightly to peer into the maw, keeping an eye on my depth so as not to rise too fast. Drysuits insulate against the cold water with air, that expands during ascent and if not vented can cause an uncontrolled and dangerous rocket to the surface. I vent some air from the shoulder valve and hover at 50 feet. The long swim tired me and my air tank is now half-empty. The Rolex shows 20 minutes gone. Time to turn back for the bow.

Over the years, the Sea-Dweller evolved. Rolex improved its depth rating from 610m to 1,220m, and gave the watch a sapphire crystal and more corrosion-resistant 904L steel. In 1988, COMEX divers set a record for an offshore diving depth while fitting pipeline at 534m in the Mediterranean Sea. They were wearing Rolex Sea-Dwellers. Four years later, another COMEX diver simulated a dive to 701m in a hyperbaric chamber and was also wearing the watch, a feat used to great effect in Rolex advertising. The Sea-Dweller had no equal and its status made it a legend and a cult favourite. But then Rolex discontinued it. Despite the introduction of the bigger and even more capable Sea-Dweller DEEPSEA that replaced it in 2008, dive watch fans mourned the loss of this original tool watch from Rolex’s lineup.

At Baselworld in 2014, Rolex revealed an entirely new Sea-Dweller to a gushing reception. The Sea-Dweller 4000, as it is called, picks up right where its forebears left off – a 40mm case made from 904L steel, the trademark gas release valve and 1,220m of water resistance. But while the prior Sea-Dweller belonged to an earlier generation of Rolex dive watches, the new one bears the traits of a new era. Wider lugs give the watch a burlier profile, an engraved ceramic timing bezel replaces the now-quaint old painted aluminum one, and inside ticks the Rolex calibre 3135 with a blue Parachrom hairspring that is immune to the effects of magnetism. The steel bracelet is a quantum leap forward from its historical forebear. Solid links are held together with screws and the clasp has a foldout dive extension as well as Rolex’s Glidelock adjustment mechanism that allows for quick fine tuning. While many newer dive watches have adjustable clasps, none are as easy to use as the Glidelock, even with the 5mm thick lobster mitts I was wearing diving in the Mackinac Straits.

I reach the Cedarville’s bow with five minutes’ dive time to spare, enough for my ascent and a three-minute safety stop to decompress. As I drift slowly upwards, past the pilothouse, then the huge hull, I emerge from the wreck’s shadow into daylight filtering down from above. I grip the yellow mooring line and follow it up until my depth gauge reads 5m, where I pause. With fingers numbed from 40 minutes in icy water, I spin the Sea-Dweller’s bezel to align the minute hand with the zero mark and start counting down my three-minute stop. Below me I can still see the faint outline and dark mass of the Cedarville. The Rolex’s sweep seconds hand smoothly finishes its third lap around the dial, telling me time is up. Hand over hand, I ascend the few remaining metres, popping up into what has become, in three quarters of an hour, a sunny day. Over my shoulder I can see the glint of traffic on the bridge, a mile – and a world – away.

Rolex