A snippet about anti-tank effectiveness during WW2.
Barrie Lovell on Anti-tank Guns
IIRC correctly the Soviets reckoned that each anti tank gun would kill a couple of tanks before it was destroyed itself. german atk guns frequently got off half a dozen shots while the tank struggled to return fire or drive out of the line of sight. A well sited gun was a far more efficient tank killer than a tank IMHO, and both the Soviet and german armies made effective use of them.