U.S. S Class / When: December 17, 1927 / Where: Off Cape Cod, Massachusetts

S-4 sank after it was accidentally rammed by the U.S. Coast Guard cutter Paulding. Paulding’s bow sliced into S-4, allowing water to flood the inner hull. Six men survived for more than a day, but rescuers, hampered by fierce weather, were not able to save them. All 38 men aboard died.

To prevent similar catastrophes, the U.S. government improved their navigation regulations and created escape and rescue devices for submariners such as the Momsen Lung and the McCann Rescue Chamber.

U.S. Balao Class / When: August 25, 1949 / Where: Off Norway

During a polar gale, Cochino could not properly ventilate its charging battery, which led to a build-up of volatile hydrogen gas and to a string of explosions. Fires disabled and eventually sank the submarine. A nearby sub, Tusk, was able to safely rescue all but one man from Cochino amidst violent conditions, but Tusk lost six of her own in the process.

The incident drew attention to the importance of monitoring hydrogen levels and keeping sub batteries ventilated during charging. It also highlighted the risks involved in an open ocean rescue during a storm.

U.S. Balao Class / When: February 11, 1969 / Where: Off Cuba

Due to a partial power failure, the stern planes (wing-like devices that help the sub dive and climb) on Chopper were stuck at a diving angle, causing a nearly vertical—and nearly disastrous—dive toward the seafloor.

Blowing the water out of the bow ballast tanks reversed but overcompensated for the problem, causing a violent and near-vertical bow-first breach at the surface. A large part of Chopper’s hull jutted out from the water. The sub then slid back into the water stern-first before finally coming to rest on the surface. The event severely damaged the sub, ultimately causing it to be decommissioned.

The incident improved understanding of how to control a moving submarine during a crisis.

Soviet Yankee I Class / When: October 6, 1986 / Where: Northeast of Bermuda

On K-219 a missile hatch leaked, allowing in seawater that reacted with liquid missile fuel that had leaked into the missile tube. The resulting explosion and fires killed four crew members. Others aboard were rescued, and the captain scuttled the sub because it could not be towed.

The accident highlighted the hazards of using liquid missile fuel aboard submarines.

Soviet Alfa Class /When: August 8, 1982 / Where: Barents Sea

The Soviets learned the hard way that liquid-metal-cooled nuclear reactors and submarines do not mix. The more common method of cooling reactors with water requires great pressure to prevent boiling. Liquid-metal mixtures have extremely high boiling points, so they can cool reactors without dangerous high pressure and they provide more power from smaller reactors. But they have drawbacks.

A liquid-metal reactor on K-123 nuclear attack sub sprung a leak, allowing the liquid metal to seep out, solidify, and create a large mass that damaged the internal mechanisms of the reactor. The sub was forced out of commission for eight years.

Soviet Mike Class /When: April 7, 1989 / Where: Norwegian Sea

While the nuclear submarine Komsomolets was operating at sea, a major fire broke out in one compartment and quickly spread to another. Power was lost and the reactors were shut down. The ship surfaced and radioed for help.

The crew decided to let the fires, contained in the two sealed compartments, burn themselves out, but the extreme heat melted seals in the hull, allowing water to rush in.

As the submarine began sinking stern first, and some 50 men tried to climb onto a life raft meant to hold 25. In the icy waters of the Norwegian Sea, the men in the water would not long survive.

Those remaining aboard the submarine attempted to escape in the emergency escape capsule, a design feature found on only Soviet nuclear submarines. The capsule failed to release until a jolt apparently freed the capsule.

The capsule shot to the surface, where its hatch burst open. The pressure inside ejected two men, one of whom survived. The capsule quickly sank and those remaining inside died.

Of the 69 men aboard, 42 died, but only 4 were killed by the fire and explosions. The rest either drowned or died from exposure. The accident highlighted the hazard of fire aboard a submerged submarine, as well as the importance of a swift rescue response.