What a difference 5 decades make, eh?
I have plantar fasciitis, which is not much different in it's effects from a heel bone spur when either/both have been irritated. Last April I did a 10K (6.22 miles) that was flattish, with a few rollers. Later that afternoon and night walking was very painful, and the next day I could hardly walk at all for the pain. This was triggered by my choice of shoes. I would not want to guess what the effects of "marching" 10 or 20 miles in Vietnam era combat boots would be. No sane Army unit would want a member who would be incapacitated by a 10 or 20 mile trudge through the jungle (or wherever).
Since it would not be life-threatening, I hope DUmoron spanone has a really good bout or three with plantar fasciitis, just to learn how incapacitating "little things" can be.