This is one of the hidden vehicles in the game. It can be found in the free roam mode, as well as in some of the missions.
The speed is even worse than the ambulance. Acceleration is about the same but the top speed is horrendous. It's really hard to tell when it's at its top speed because the top speed is less than half of a family car's speed.
The handling is also very poor. Although the speed is worse than a cat with a piano on its back, the handling is just as slow. If you want to turn a corner, your wheels move very slowly, mainly because the vehicle is so heavy. I wouldn't count on it.
The damage is a whole new thing altogether. It almost seems that it's invincible. Look at the name, it's called: "Armoured Car". That means it is made especially for damage. Don't get too exited, though, it can blow up. When I first drove it, I thought it would never blow up - like the tank in Vice City. But then I started a rampage and sadly... it blew up *sheds a tear*.
The armoured car looks nothing like a tank. It has wheels, and it's just a big black chunk with an engine. It can be found on Birdcage Walk, which is just next to Buckingham Palace. Check out the link above for much more descriptive directions.