Does that thing have a big turntable under there somewhere? Because from the photo, it looks like it can shoot in exactly or almost exactly the direction the rails happen to be pointing, and if you need to shoot somewhere more than two or three degrees to either side, you're SOL…
It doesn't look like it. They did sometimes use a kind of turntable to allow regular cannons to easily change direction, but I don't think the same was done with these.