The Americans and British later adopted this system. Like every new weapons development, the adoption by both sides led to the development of countermeasures. The basic acoustic countermeasures the Germans used (particularly ensonification bubbles, called pillenwerfer) are still in use today.
Other systems include passive decoys, to lure homing torpedoes away. The goal is to buy enough time for the submarine to escape the torpedo. Another method is the mobile submarine simulator. Getting the enemy to shoot at the wrong target is never a bad thing. Not only has he wasted ammunition, but hes probably given you a good idea of where he is. And that can be fatal.
Surface vessels have also developed countermeasures. Often these are towed decoys, which will be single-use. The first of these was the Fanfare, which was later supplanted by the Nixie. These decoys gave off noises that resembled those of the ships towing them or those of larger vessels. The hope is that the torpedo will go after the decoy and not the real ship. These are known as soft kill systems. However, the soft-kill concept has a huge problem. Decoys might work too well, as was the case when HMS Antelopes chaff decoyed an incoming Exocet missile into the ship Atlantic Conveyor. There is another problem. Soft kill systems can be countered. Once acoustic countermeasures became reasonably reliable, and workable, the response was to design torpedoes that were not vulnerable to countermeasures. Say, a torpedo that would home in on a ships wake. This tipped the edge back in favor of the submarines.
The Russians, who often faced superior Western sensors, began developing hard-kill systems. These were initially variants of the RBU anti-submarine rockets (an ahead-thrown weapon similar to the Hedgehogs of World War II). The Americans have gone with a new twist on this concept. Old Mk 46 torpedoes are being updated to the Mk 46 Mod 7 standard. This system, though, does not hunt submarines. It hunts torpedoes, instead. A wake-homing torpedo might not be decoyed, but it also is unable to take evasive maneuvers. This is called the hard kill concept, and it is ultimately the best way to deal with anything incoming. The specter of the Atlantic Conveyor makes that clear: A soft kill system can spoof a weapon into hitting another escort or the merchant vessels that the escorts are there to protect. A hard kill system makes a threatening torpedo go away for good. Permanent solutions are preferable when a torpedo (or any other weapon) is inbound.
The new generation of American littoral combat vessels is currently under development. These ships will be faster than current naval vessels (some concepts boast top speeds as high as 92.6 kilometers), and will have a better chance of outrunning a torpedo. Like many other areas of warfare (such as tanks vs. ATGMs, and SAMs vs. aircraft), the competition between the submarine and the surface ship as to who will have the edge. Harold C. Hutchison (firstname.lastname@example.org)
Submarines now have more advanced torpedoes than they did in World War II. This has made life much more dangerous for surface vessels and other submarines. Yet, countermeasures have become more formidable as well. Starting during the World War II Battle of the Atlantic, the first torpedo defense was to make a hard turn towards (or away) from the torpedo. Maneuver out of the way, and then go after the impudent submarine with depth charges. However, the German response was to develop the first homing torpedoes. These would home in on the sound of the ships engines, often aimed at the escort ships. It was a logical approach even if the torpedo did not hit, the escort was forced out of position, allowing the firing U-boat (or another U-boat in the wolfpack) to get a shot at the merchant vessels.