Dozywannabe,
Not suggesting conspiracy. Just suggesting 3 entities that hoped that each other didn't get too clever or creative, too soon, as long as they all had plausible deniability. "How were we supposed to know the sub didn't know to detect 37.5 khz specifically. After all, a 5th grade science student would have known it"
I agree that malice shouldn't be assumed if stupidity will suffice, but it took France long enough to ask for help.
Chu Chu,
True. Sonar was not optimized for 37.5 khz, but if it were, it's range would have been multiplied tremendously. There's no comparison in sensitivity when tuned specifically to it, rather than listening to a broad dynamic range. Could have used a hetrodyne setup. One of those Albert Michaelson type things.