The USMC. Josh told me that they spend pretty much their whole lives cleaning them after any amphibious use, apparently they're real nice pieces of machinery but prone to breaking down if not constantly kept up.
That one's nutty, it looks like it's an M48 Patton, but has one too many roadwheels. But sure as shooting that's a Patton series turret. I don't imagine I'll be able to look for the answer anymore today, got me a class to teach. So good hunting to the rest of you.