Supposedly you can run on pavement barefoot, after a lot of acclimatization. You natural stride (toe first vice heel-first) absorbs the impact so it just comes down to wear and tear on the soles of your feet. Shoes cause us to land heel-first when running, so it takes a while to get used to doing it the other way.

I used to walk barefoot several blocks to surfing every day and my feet toughened up pretty good. I think they are supposed to be able to do that...but all of our shoe-wearing keeps them tender.

I don't know if they get tough enough to protect against glass or nails, but those five-finger shoes would take care of that issue.

I'd probably try it if I had a long enough stretch of grass, sand, or dirt trail but I don't, so I may just stick with shoes. I'm not sure what the navy would think of barefoot fitness tests.