Watched "The Enemy Below" last night...

[Vaux]

...for the first time in about 3 decades (seriously). What a great movie, but my what a spotlessly-clean and spacious UBoat Curt Jurgens had!

One question: Jurgens' character used some kind of "ink discharge" to confuse the DE's sonar. Mitchum's character referred to is as "using a decoy". It wasn't oil because it didn't float to the top and appeared to disperse in the water. Is this historically accurate? If so, what was it?

[Platapus]

In the movie, the Germans called it Bold. It was also called Pilenwerfer

http://en.wikipedia.org/wiki/Pillenwerfer

I think the reason it was coloured like oil in the movie was so that it could be easily seen by the audience. The Bold would "fiz" and make bubbles which would probably be difficult to reproduce on the screen and would be difficult for the audience to appreciate.

Here is another reference link http://www.uboataces.com/sonar-decoys.shtml

[Vaux]

Thanks, Platapus. Interesting info.