Gershon, thanks for the link to the combat boot tests. I found it interesting that this 1992 study found that jungle boots also had no water penetration during the 15 minute test when the eyelets (drain holes) were plugged. I have no experience with modern combat boots, but I definitely do with jungle boots; I still have a pair of those in my closet from the 1970's.

I think the significant factor here is that these were static tests on "unworn" footwear. I've got to believe that the mechanical action of walking in ('worn') boots across an deep and extensive creek or river crossing would result in something quite different, at least with jungle boots (even with eyelets plugged).

It also wasn't clear to me in that test just how the boots were submerged, but I came away with the impression that they were held so that the very top of the boot wasn't under water. I.e., that they weren't testing water infiltration from the very top down when worn on an actual human foot (and ankle).

I don't mean to hijack the thread with this, nor to seem to contradict your personal experience (!). But I remain skeptical that extensive and deep water crossings would allow no water to get in, and particularly I wonder if some sort of regular cleaning and reapplication of waterproofing or the like is part of the magic. With trail runners, I'm sometimes out for weeks or months at a time, and definitely doing no "maintenance" unless something is very overtly failing.