Quote:
Originally Posted by NightCrawler
So the British came up with hydrophone, and the German use it against them?
Because Hydrophone had a longer range than Sonar.. so the German knows who ever is nearby than the Destroyer....
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Let's not confuse the terminology and function too much. The difference you're suggesting here is between hydrophone aka. passive sonar, versus ASDIC aka. active sonar. The two have very different methods of detection, although fundamentally both do use sound waves and piezo-electrics to do their job. They are crucially meant to be used in a way that's complimentary.
Nearly all escorts you encounter are equipped with passive sonar/hydrophone, and they're listening just as carefully as you are. Just that the sub can generally afford to be a lot quieter than surface warships, and being far away from the "messy" surface waves does help clarity and range for hydrophone contacts. However this does not mean that surface escorts wouldn't be listening. Now, it's useful as long as whatever you're hunting is making a sound. As soon as it stops - you're kind of on your own there...
Active sonar, on the other hand, can detect large objects irrespective of the noise they're making. These can be also mounted on anything, but for obvious reasons the WWII submarine is not best-advise to emit the loud sounds needed by active sonar to work, because they'll be picked up by those hydrophones that ASW ships are listening for you with.
The submarine always has an advantage in terms of acoustic stealth, but not because of its hydrophones being superior. You can more or less assume that enemy ASW ships will have the same kind of hydrophones as you. It's mainly because the submarine is a quiet platform in normal modes of operation that you have advantage - yeah, you'll hear those escorts first, not because your "hearing" is better because they sail faster and make a heck of a lot more noise than you do. And there's not much they can do about that except outright stop. Which was by the way a tactic used by persistent sub hunters.
Otherwise, at the start of WWII, hydrophone capabilities weren't too far apart between nations. These were a well-established technology, and at least on submarines, did not really evolve much until after the war, when passive sonar operation became a much finer art. The german U-boats maybe had a slight edge, but it was mostly because of the number and quality of 'mics' in their hydrophone arrays, and their cleverly overlapped use of two different different sets of sensors on the top and bottom side of the boat for listening (the GHG and KDB). Everyone else had reasonably good hydrophones available though, both for submarines and ships hunting them.
As far as the Americans, aside from generally operating near the surface or on the surface, there were a few advantages they had. Firstly, US subs' hydrophones consisted of rotatable 'mics' mounted on the bottom of the sub. In theory, they worked on the surface, though in practice the sub needed to be both running slowly and in reasonably calm seas for that to work. Otherwise they certainly had listening capability approaching that of Germans.
But the real strength for the American subs was their radar, which among other things could be operated from periscope depth. The US subs relied extensively on their radars, rather than acoustics, for detecting enemy ships. This is something Germans were far behind in, and unlike the US subs, U-boats never received effective radar capability in any numbers.