The Ocean Ranger was, in its day, the largest Mobile Offshore Drilling Unit in the world. One toolpusher called the rig "unsinkable" (note to anyone offshore- if it floats, it can sink). The loss of the Ocean Ranger was one of the biggest disasters in the history of the oil industry.
The Ocean Ranger, owned by ODECO out of New Orleans, was under contract by a Mobil subsidiary off the coast of Newfoundland. A ferocious storm came up. After bracing for the storm, the men aboard thought they were safe, but a rogue wave smashed a porthole and flooded the ballast control panel. Between an under-trained crew and a serious design defect, the platform capsized in heavy seas that it should have been able to handle.
Some of the crew was washed into the water. Some got into lifeboats that were ripped to shreds as they were lowered. One boat, however, with approximately 20 souls made it down safely. A crewboat on standby at a nearby rig made a heroic effort to save the men in the water, but the frigid waters incapacitated the men in the water in seconds. ODECO deemed it too expensive to equip the rig with survival suits. The men on the crewboat, despite their best efforts, had neither the equipment or the training to rescue unconscious men from the heavy seas.
The one intact lifeboat was found by the M/V Seaforth Highlander. The crewboat lashed lines from the lifeboat and the men on board were just a couple of feet from safety, however the lifeboat depended on the men on board staying strapped into their seats for ballast. The lifeboat slowly capsized. All the men were washed into the water. The captain of the Seaforth Highlander described it as "watching a slow motion movie." All the men in the lifeboat were quickly overcome by hypothermia and drowned.
Every single crewman aboard the Ocean Ranger died. Only couple of dozen bodies were ever recovered, despite extensive search efforts.
The USCG Board of Inquiry [PDF] describes the incident in much, much more detail. I highly recommend it.
The USCG report comes up with a number of findings. A few I'll mention briefly:
* Insufficient training. Ballast Control crewmen only had basic, on the job training. They had no classroom training and didn't understand the working principals of the pumps. The ballast system also went into a "safe" mode in case of failure whereby all ballast compartments are sealed. It appears that the crew misunderstood a bypass system and unintentionally worsened flooding.
* The crew of the Ocean Ranger didn't call for help until it was deep into the storm. Once they did abandon ship, the Ocean Ranger actually stayed afloat for at least another hour. The crew died while the rig was still afloat.
* There was a critical design flaw that was completely missed by the designers and regulatory bodies: the chain lockers, storing the anchor chain, were open to the sea and un-sounded. The crew had no way of knowing if the chain lockers, an enormous void that could cause the rig to list or capsize if filled, had water in them. They had a 5' hole at the top for the chain to enter that had no way of closing off or sealing from the weather.
Inviting Disaster (thanks for the rec, PE) has a chapter on the Ocean Ranger. It closes with one interesting observation. The Ocean Ranger had drilled in the Baltimore Canyon off the East Coast. It drilled off the coast of Ireland. It drilled offshore Alaska. It had just begun drilling off Newfoundland. The largest, most advanced drilling rig of its day never once struck oil.
Couple notes to tack on the end:
* Here's an archive of Canadian news broadcasts about the sinking.
* Ocean Ranger had a sister ship. It was originally named Ocean Ranger II, but was renamed Ocean Odyssey while still in the shipyard. It suffered a well blowout that ended its oil drilling days. It now serves as a satellite launch platform as a part of the Sea Launch system. It's still operational, despite one rocket that blew up on launch.