When submarines are lost, they are said to be "on eternal patrol." This comes from the fact that many times, the term submariners use for deployment is "patrol," a term that predates World War II (a 1938 movie focusing on a subchaser was called Submarine Patrol). A combat deployment is often called a "war patrol," and American ballistic missile submarines are on "deterrent patrols."
These patrols begin when a sub leaves port, and end on their return. When a sub sinks, and doesn't make it home, the patrol is "eternal."
The loss of a peacetime submarine is not unheard of. Since the end of World War II, the United States lost four submarines. Two, the nuclear-powered attack submarines USS Thresher (SSN 593) and USS Scorpion (SSN 589), were lost with all hands. In the late 1940s, two Balao-class diesel-electric submarines, USS Cochino (SS 345) and USS Stickleback (SS 415) also sank as the result of accidents.
The United States has not been alone in losing submarines. Most famously, in 2000, the Russian nuclear-powered guided-missile submarine Kursk, an Oscar-class vessel, suffered an on-board explosion and sank with all hands. The Soviet Union had five nuclear-powered submarines sink, albeit one, a Charlie-class nuclear-powered guided-missile submarine, was raised, and they lost other subs as well, including one in a spectacular explosion pierside.
It sometimes can take a long time to find those subs. A Whiskey "Twin Cylinder"-class guided-missile submarine that sank in 1961 took over seven years to find. The Soviets never did locate the Golf-class ballistic missile submarine K-129 until investigative reporter Jack Anderson revealed the existence of Project Azorian.
While the cause of the explosion that has apparently sent the San Juan and her crew of 44 to the bottom of the South Atlantic may never be known, what is beyond dispute is that submariners face a great deal of danger – even when carrying out routine peacetime operations.
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