Real WW2 submarine sounds

[Highbury]

Originally Posted by MuscleBob.Buffpants

The quality of the 2nd wire is a bit better than the first. If you listen real careful (with headphones) you can hear a faint "chu-chu-chu" sound. That's the sound of the props of the I52.

Originally Posted by HNSA Site

Note that I-52 had already been sunk by the first aircraft. The propeller noise heard are from a German submarine in the area.

You are quite correct in identifying the sound, just not the source. It is interesting to note that the crew of the aircraft also thought the same as you.