World War 2 History: The Only Time in History a Submerged Submarine Sank Another Submerged Submarine

In movies and books about the Cold War and whatever era we are in now and wherever we're going, it is not uncommon for two submarines to fight each other deep below the ocean's surface. Usually, one emerges victorious, while the other, holed or blown to pieces, disappears into the freezing, inky depths below. In actuality, there is only one documented instance in history of a submerged sub attacking and destroying another submerged sub.  Link
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