It sounds like a combination of the following:
Arnie 2 (isometric view)
Fernandez Must Die (top down, tanks, rescuing prisoners)
Ikari Warriors (top down, with tanks that explode)
But to me the game that most resembles that description would be Rambo on the C64 - isometric view, blowing up walls and buildings, rescuing prisoners from the camp. A search for isometric shooters in HOL yields little that matches this description unfortunately