To control its exact movement you'd need to initialize it then move it with a periodic timer based on an offset value (i.e. move it 10 units every .03 sec in a certain direction).
However, a very basic moving "missile" could be a unit w/ flying, no collision or the locust ability, and fixed height values. However, it can only reliably move short distances else it will most likely move in a zig zag pattern as it calculates pathing (particularly at any odd angles that are far away).