Also it doesn't form a vacum bubble around the torpedo. That would be impossible. It creates an air bubble around the torpedo.
Many US sites write off the Shkval as something of an anomaly. AFAIK the Russian's have always portrayed it as a revenge weapon, something to throw back at the other guy so he loses control of his own torp if wire guided and not a primary first strike weapon. Of course it could be used as this if enemy sub is found first and is close by.
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