I’m not wholly ignorant of military affairs, but I must express puzzlement on a relatively basic matter. I often hear that “Castle X commanded the Y valley, and so Z and his army could not go that way.” Now, that makes sense to me if the valley is very narrow and the army cannot physically cross it without running up against the fort, or if the fort has artillery of some sort whose range can cover the valley. But this is often not the case; often in the cases being referred to, the area is miles wide, and the fort’s weaponry has a range far less than that.
To pick a concrete example, while in the Florida Keys recently, I was reading about how a fort was built in the Dry Tortugas. The original purpose of it was, I was told, “to protect the Gulf ports.” But this makes no sense to me. The passage between the Keys and Cuba is 90 miles wide; if I intend to take Mobile or Gavelston, I simply keep my fleet out of the range of the guns and proceed onward.
Please note that I’m not referring to the capacity of forts to act as strong points in a defensive line, as observation posts, or as the base of operations from which forces may sortie. Those I can understand. What I’m struggling with is the putative ability of forts to control an area larger than that which they can directly project power onto.
I hope that makes sense. And yes, I know what Patton said; my question is why anyone ever thought differently.