Environment: Operations: Military

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Navy and Coast Guard surface ships do not routinely cruise the heart of the Arctic Ocean, but submarines have historically used sea ice as the perfect cover to hide from surface ships and aircraft.

German U-boats used sea ice as an escape route after attacking ships on the Russian coast during World War II. When the Cold War emerged, submarine operations in the Arctic became a crucial part of strategic defense for the United States and the Soviet Union. In 1958, the U.S. submarine U.S.S. Nautilus was the first submarine to reach the North Pole and traverse under the ice across the entire Arctic. The cover provided by sea ice and the location of the Arctic Ocean--bounding the U.S. and the Soviet Union--provided the potential for submarines to surface through the ice near each country’s coastline without warning, and launch missiles.

Sea ice can present a navigational hazard for submarines, which typically travel near the surface, and crews are always on the lookout for keels from ridged sea ice that may cause severe damage. Also, while some submarines in the Arctic have features to help surface through the ice, they still cannot surface through ice that is greater than three meters (nine feet) thick. Submarines that are not ice-strengthened can only surface through ice that is less than one meter, (three feet) thick. Submarines must be able to quickly locate leads or thin ice to surface quickly during emergencies, to send messages, or to launch missiles.

Sea ice also plays an important role in submarine operations because of the ice’s acoustic properties, the way it interacts with sound waves. Submarines use sonar, or pulses of sound waves, to “see” the area around them. Sonar is particularly critical in finding enemy submarines and obstacles to navigation. Sea ice cracks and groans as it moves around on the ocean surface, creating an acoustic signal that interferes with the signals detected by the submarine’s sonar. Plus, the bottom of the sea ice reflects signals from other, nearby objects, which makes it difficult to interpret sonar returns. Sea ice can help a submarine avoid detection from an enemy submarine, but it can also impede attempts to track the enemy’s location.

The end of the Cold War in the 1990s reduced the need for intense submarine operations in the Arctic. However, the U.S. Navy still conducts operations under the ice.

In the 1990s, several scientific cruises took place as part of the Scientific Ice Expeditions (SCICEX). These operations were military in nature, and most details remain classified. However, submarines participating in SCICEX collected many sea ice and ocean observations that are otherwise difficult to obtain. The most important observations in regard to sea ice were estimates of ice thickness from an upward-looking sonar. A comparison of recent data with data from submarines in the 1950s through the 1970s shows that sea ice has thinned by about 40 percent. See the sea ice section of NSIDC's State of the Cryosphere for further details on thinning sea ice. NSIDC archives and distributes data from Scientific Ice Expeditions (SCICEX). You can also visit Submarine Upward Looking Sonar Ice Draft Profile Data and Statistics for more information.

Decrease in Arctic sea ice draft from 1958 to 1997. Graph derived from Rothrock et al. 1999.