Those 345 MPH Supercavitating Torpedoes: Did You Know?
UPDATE: July-10-2008 - Related posting about cutting edge research: What If ...? .
The Peoples Republic of China reportedly bought 40 Shkval rocket torpedoes from Kazakhstan. in 1998. An improved version of the Shkval may be capable of a 300 knots speed (345 mph).  France, the U.S., and Germany have also undertaken supercavitating torpedo development.
With a range of at least 3 to 4 miles, Shkval torpedoes reduce reaction times to travel that distance from 3 minutes to perhaps 40 seconds. The swiftest traditional undersea technologies, in contrast, are limited to a maximum of about 80 mph. Scientific American published an article Warp Drive Underwater in 2001: When the Russian submarine K-141 Kursk sank last August, rumors surfaced of mysterious blasts sending the huge sub to the bottom of the Barents Sea and that this was somehow connected to testing an ultrahigh-speed torpedo. "Several months earlier, when American businessman Edmond Pope was arrested in Moscow on charges of espionage, it was said that he had been trying to buy the plans for an ultrahigh-speed torpedo."
The missile has been characterized as a "revenge" weapon to be fired along the bearing of an incoming enemy torpedo. The Shkval may also be considered an evasion torpedo, which when fired in the same direction forces the attacking enemy to react evasively (snapping their torpedoes' guidance wires). Russia began marketing this conventionally armed version of the Shkval-E(xport) high-speed underwater rocket at the IDEX 99 exhibition in Abu Dhabi in early 1999.
Certainly, the technology has its own drawbacks. The supercavitating torpedoes noise and speed are two of the drawbacks, limiting sonar homing and wire guidance possibilities from the outset. The Shkval-2, however may overcome real-time guidance feedback, nevertheless.
Should sailors be particularly frightened of this continually improved torpedo? Perhaps, but submarine sailors will not be frightened, because controlling very hazardous conditions, or else, has always been a day-in and day-out necessity for them.