Sound buoys
 

Just read Iron Coffins by Herbert Werner and in the book he decribes how, while piloting an u-boot near the coast of Ireland in September -44, he encounters sound sources sounding like propellers and sonar pings. Further on as he checks the surface to be empty of ships, he explains these sound sources are buoys that generate sound scattered around the coast to drive u-boats further to the sea.

I searched information about these kind of devices used by the British but could not find any.
If anyone knows about these, I would be interested to know how they worked: did they run on batteries, did they had radio recievers etc.
Also would be interesting to know what countermeasures the Germans took on these if any.

I've not heard of a separate bouy that produced sounds as described. The British did use what they called "foxers", a sound generator towed behind a ship to fool acoustic torpedoes.
https://en.wikipedia.org/wiki/Foxer

I looked at NavWeaps without success, but you might have better luck.
http://www.navweaps.com/index_tech/index_tech.php

He could have been picking up a CZ contact, seems the most likely to me.

No hits for me either, but thanks for this interesting site!


What is a CZ contact?

I'm guessing if it has any basis in real life he might be describing a 'duct' where sound gets bounced between the surface and a temperature layer to be detected a lot further away than you'd expect. (They model this in Cold Waters). I haven't heard of any noise maker like this in WW2 and I doubt the technology existed back then in a way that would be practical.

Iron Coffins is not a very historically accurate book. There's a ton of downright whacky stuff in it that is clearly bull****. Nobody is quite certain if Werner was just embellishing things, mis remembered what happened or an overzealous editor/ghost writer tried to spice the story up a bit.