Randomizer

Well considering that there is not a single reliable account of a successful sonar only attack in the entire Pacific war, why are you surprised that yours failed?

Solving the target motion analysis problem with whiz-wheels and manual plots alone can never be effective although repeated often enough it might yield a success or two.

Only in the artificial world of SubSim is the technique alive, in the event the USN held the sonar only approach as doctrine until just after actual war started and then dumped it almost immediately as it did not work.

What you're experiancing is just the game imitating real-life.