I mentioned the common, nonsense definition of "hydrostatic shock" primarily to find out what Angus meant. You're absolutely right, it doesn't mean anything, but was a term promoted by many people during the early days of very high velocity cartridges, one of the biggest promoters being Roy Weatherby. As some people have pointed out in the past, even the term "hydrostatic" doesn't apply, as there's nothing static about it.
Roy Weatherby promoted hydrostatic shock with very high velocity bullets as THE answer to killing power. According to Weatherby, arteries and veins acted like brake lines, transmitting the impact of the bullet to the brain, killing animals no matter where the bullet landed. But he first formulated this theory (or followed the lead of other proponents) after having only killed a few deer. When he started making money on his rifles, he went on an African safari that supposedly would demonstrate hydrostatic shock on many animals. It didn't, and you can read all about it in the biography of Weatherby written by Grits and Tom Gresham, which contains a bunch of Weatherby's African journal. In fact ultra-high velocity with cup-and-core bullets was a dismal failure, especially on larger animals, and in his journal Roy keeps backpedaling by modifying his theory.
From my reading on bullet tissue-damage, cavitation can be a major factor in creating a larger wound channel, but it still isn't enough to short-circuit a deer's brain with a hit in the butt. What any of this has to do with tanks is a mystery.
P O Ackley did his part to popularize the myth of hydrostatic shock when writing of .17 caliber rifles. "Hydrodynamic Shock" would have been a better term, but wouldn't change the physics that don't exist.
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