This all beside the fact that, of course, a sea borne assault of Gibraltar would be suicidal with land units only: the guns at Gibraltar would sink whatever thing which can transport land units before it reaches the shoreline. (I'm not an expert, so I do not know if there is any blind spot anywhere, but I doubt that there is any one or that would make a difference in this case.)
The question, in this case, would be whether or not the guns can be silenced with battleships and/or huge bombs, to make the landings possible at all.
Of course, this would be even more special rules for Gibraltar: I'm not proposing them, just saying.
