This thread really isn't the place for any "real" information, but at the least the notion of a "closing" contact might well have been possible in ww2, no? Assuming attenuation and other factors related to transmission of sound through water stay relatively constant during the time frame from observation 1 to observation 2, might it have been possible to decide the target was closing simply based on signal strength increasing? This would just be a "closing" vs "receeding" distinction, nothing with the fidelity to get a range-rate.
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