If they're in trenches, they aren't exposed. If they're not exposed, they can't shoot, and there's no point in firing up their engines. If they don't shoot, and they don't fire up their engines, they might not be noticed. If they're not noticed, there has got to be at least a .01% chance they won't be turned into smoking charnel houses, the interior of which are coated with a thin, greasy paste that once was their crew.
Sound to me like they've learned a lot. *grin*
Nahh. It seems like during Gulf War I the chopper pilots called it "Tank Plinking".
They figured out that the tanks retain their heat LONG after the surrounding desert does. So if they went out at night with an infrared filter, the tanks showed up in a bright white (well bright green with the night vision stuff) :)
So even if we didnt know where they were, they ARE findable.