Aye! There is, and its not what you mention.
I don't know how you do things in the Army, but in the Navy, we have a whole bunch of contingency plans for all sorts of things, the are called (or used to be called) MAOP's (Maritime Operations Plans). And there is one for Harbour Defense, and there is one for Coastal Defense. I know because before my retirement, I had worked, with many others, on their updating, and served for a term as the assigned Coastal Defense Sector Commander for a given sector.
So, no, the plan is NOT to wait for a threat to occur and then "figure out" what to do, or "conjure up" a response. It's all been done and can be activated if and when needed.