A 1966 study by the U.S. Navy noted that "The passage of large-amplitude internal waves could make submarine depth control difficult, particularly when the submarine is running quietly at low speed." The report, titled Internal Waves: Their Influence Upon Naval Operations, added that such waves "could initiate uncontrollable sinking of a submarine."

In World War II, submariners avoided the Strait of Gibraltar partly because they were aware of its reputation for propagating unusual undersea waves that were considered hazardous, David Farmer, a physical oceanographer at the University of Rhode Island, told USA Today in 2014.

At the height of the Cold War in 1984, a Soviet submarine that was apparently running beneath a tanker to mask its exit from the Strait suddenly smashed into the tanker's hull, causing damage to both vessels and forcing the submarine to surface. The collision is thought to have been caused by an internal wave that unexpectedly thrust the submarine toward the surface.

The waves "are generated over steep topography due to the surface tides," he tells NPR. "In the South China Sea, internal wave amplitudes can be about 100 meters (330 feet)."