Here’s the flip side. The silo is at a fixed location, and found by reconnaissance satellites (hell, google earth). Now where is that bloody submarine?
Track it from when it leaves port.
There are considerably more than 400 silos. Most of the silos are dummy silos, which contain a working Minuteman III but it has no nuclear payload. The missiles that have the nuclear payload change. To guarantee that you take out every one of the 400 Minuteman III missiles that have a nuclear payload you would have to hit every silo. Which is quite a few of them. Our SSBNs while difficult to track are not impossible to track, and we have only 14 of them.