I don't think i would want to be shot at with a tank.
Flying from the barrel of a gun.
That's why you shoot one back and have them cancel eachother out in mid-air, perhaps squishing some other people when they fall

You want to launch vehicles at people? 
Precisely!
Well the limit still isn't 20.
Okay, but still go with the idea of 1 per time, as that limits the number of possible additional vehicles to 32.
Unless they bring out another one of the launchers in the mean time?