What submarines do while on patrol.

What submarines do while on patrol.

What submarines do while on patrol.

Answers to your questions about the news.
Aug. 6 2009 6:13 PM

What Do Submarines Do on Patrol?

Watch other ships, or just look intimidating?

A submarine. Click image to expand.
A submarine

Two Russian submarines have been "patrolling" about 200 miles off the East Coast of the United States, administration officials acknowledged Wednesday. The Pentagon was quick to reassure Americans that the presence of the submarines was neither extraordinary nor threatening. What exactly do submarines do on patrol, anyway?

It depends on the type of sub. Fleet ballistic missile submarines, which are armed with nuclear warheads, have only one job: to stay put in an assigned area—insiders call this "drilling a hole in the ocean"—and await orders to fire. Attack submarines, on the other hand, carry conventional rather than nuclear weapons. They support ground troops with cruise missiles, engage enemy naval ships and submarines using torpedoes, and sometimes transport commandos who need to sneak ashore. The deployment of attack submarines during peacetime sends a reminder to competing navies that they do not have free rein over international waters. The Russian submarines deployed near the East Coast—probably attack submarines, given the lack of alarm from U.S. officials—were likely monitoring ship movements and projecting Russian naval strength.

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When not engaged in combat, attack submarines patrol the open ocean or a "forward area"—for the United States this commonly includes the Persian Gulf, the Mediterranean, the Western Pacific, the Soviet Arctic, and the Sea of Okhotsk. Patrols usually last for 30 to 60 days. (The limiting factor isn't technology; it's people: A nuclear-powered submarine can operate for years without surfacing, but the crew would get restless and very hungry long before that.) Most patrols are intelligence-gathering missions. This usually means observing the naval exercises of other countries or tracking the movement of a naval vessel or a commercial ship that is carrying sensitive cargo.

Sometimes the Navy will deploy attack submarines to monitor activity in and out of a foreign port or even to watch something on land. The latter task can be tricky because submarines still rely on periscopes for above-water reconnaissance. Granted, periscope technology has come a long way from the old double-mirror design—many ships now employ both optical and digital instruments that provide 18x magnification—but the field of vision is still limited to only a few miles due to the curvature of the planet (or less, depending on sea conditions). If a submarine is going to see land, it has to be stealthy about it because it needs to get much closer than international law allows.

Attack submarines also test new missile systems (many analysts believe a failed torpedo test sank the Kursk in 2000). But it's highly unlikely that the Russian Navy would be conducting a test so far from home.

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Explainer thanks Norman Polmar, naval analyst and author of Cold War Submarines: The Design and Construction of U.S. and Soviet Submarines, 1945-2001.

Brian Palmer covers science and medicine for Slate.