Possible Enigma application

[gurudennis]

Originally Posted by Fidd

I've read of hydrophone detection ranges of up to 100km, however, I suspect that related to the explosion of depth-charges or torpedoes. However, as it may reasonably be inferred that dc's and torpedoes exploding are in the region of the convoy, that would give a position line if not the location. Frankly I don't know the hydrophone range for detecting a full convoy, but I have to think it'd be considerably further than 10km, and probably 50km at least with a quiet U-boat?

I recall a particular statement that (I paraphrase) "visibility was so poor that it was easier to listen for targets on the hydrophone than to try and spot them from the bridge". Implying that ordinarily the range of assured acquisition on the hydrophone would have been shorter than the visual acquisition range. The latter is of course limited to about 10 km by the curvature of the Earth.

[Fidd]

Originally Posted by gurudennis

I recall a particular statement that (I paraphrase) "visibility was so poor that it was easier to listen for targets on the hydrophone than to try and spot them from the bridge". Implying that ordinarily the range of assured acquisition on the hydrophone would have been shorter than the visual acquisition range. The latter is of course limited to about 10 km by the curvature of the Earth.

I think the crux of the matter is whether one is considering picking out the bearing of a specific ship, for "targeting" or for detecting the general position of the convoy as a whole. 10km sounds quite reasonable for the former, but rather too short for the latter.

It's reasonable to suppose that the distance a convoy could be detected at, is at least the routine separation of U-boats in a north/south line across the path of convoys, if not up towards double that interval.

So the question becomes, what, historically, was the interval of U-boats when seeking to gain the 1st detection of a convoy?