Everyone's heard of the crazy Ivan. If you haven't, then you're lying. It's that maneuver in Tom Clancy novels where a submarine essentially spins around to see what's behind them. I always figured that this reckless technique was invented by some wacked-out Soviet dude, chugging vodka and doing stunts with his submarine. WRONG. MAN was I shocked to learn that not only was my scenario incorrect, but it's not even like the sudden spin-around in The Hunt for Red October or in Firefly.
The Crazy Ivan is a way for submarine to shifts their radar detection to see spots where they previously could not. A submarine basically cannot detect anything that is directly behind it, so that area is a blind spot. By performing a series of sudden movements, the submarine moves that blind spot around and can detect things previously hidden.
The "crazy" part of the name comes from the sudden movements that the sub performs, and Ivan was a common nickname for Russians, much like Charlie was for the Vietcong.
American subs would counter this tactic by going for absolute silence by shutting off their engines. The problem was that their sub would continue moving due to its momentum and could very likely crash into the other sub, which is exactly what happened in the case of the U.S.S. Tautog and the Russian sub "Black Lila."