As I said before, I have a few pointers I have come across that will keep those feet marching. First off, ID what type of boot you were issued, whether hot or cold weather. For this first part I am going to focus more on the hot weather pair than the cold.

Ok, so first things first, take on boot and try to bend it in half. Ah ha! Not so easy is it? Thats because the army came up with this ingenious plan to put something in the center so that you can flex your foot to far; pretty nifty hun? When developing the boot the Army looked at cost and came up with an ingenious plan to put a 1/2" by 4" piece of fiberglass in the middle of your boot. While this fiberglass is flexible, it doesn't allow your foot full range of motion, causing those usual cramps and tired feet. So this will be the basis of my first post; the removal of that piece of fiber glass.

tools needed
-standard, long neck screw driver
- pair of pliers, preferably some longer ones for leverage
- or a Multi-tool for those with out a tool box handy

Steps-
1) Remove the flimsy sole thats easily removable.
2) Next comes the fun part. You will be removing the next layer of the boot using your screw driver. Look into the boot (head lamps work really well here), right where the arch of your foot would be. You should see a piece of leather/cloth swoops down under neath that pad; this will be your first entry point. Take the screwdriver and pry the pad from the bottom of the boot, but be warned! That pad is not made from titanium, if you try an pry too har you will ripe the pad, and make life harder. The pad will not release from the boot so easily due to the glue and the actual rubber attached to tat pad. you only need to wiggle the screw driver into the pad about a 1/4" and then start working back towards the heal. once you have gotten to the heal, go back to the arch area and do the same thing to the other side, releasing the heal part of the pad, mostly. this is the vulnerable area because the glue is minimal there as well as only being tacked in by brass tacs, which is actually a good thing.
3) Once the heal portion is partially up, grab ur pliers, or turn around the Multi-tool, and start pulling. But again, BE WARNED! Make sure that you have enough of that pad that you dont rip off a piece of the section, if so, your life will be hell! continue pulling and soo you will see a white silvery material, this is the fiber glass in your boot. Now then, the pad is going to play hard ball from this point on, especially once you run into the tongue and are still trying to pull up that pad.
4) Once you get most of the pad out of the way, take your screw driver and pry that fiber glass out from the clutches of the rubber. Once the fiberglass bar is mostly out, you will inevitably have to use your pliers again to this time pull on the bar. Be careful of that bar though, it will splinter if you grab too hard and wiggle it too much.
5) When the bar is free, discard and then look back into the boot. You will see that the brass tacs in the heal are standing up a bit, just go a head and use your screwdriver or plier head and bend them down into the rubber. 'But doesn't that piece need to be tacked back down?' No, your body weight will keep it there and since you didn't remove the entire pad from the rubber, you wont get any slippage.  Once the tacs are pushed down, return the pad, and then add back the your sole of your choosing.
6) Now repeat for boot number two.  

Once you are complete, you will notice a greater range of motion from your boots, and soon you will be on your way to more comfortable boots that fit like sneakers.                                                                                                                      

So you have this new pair of issed boots , and you want to know how to break them in and make them feel like sneakers, dont you? I was wondering the same thing whenever I got my boots and after searching the internet far and wide, I realized there was no such information. This is where a little bit of NCO help and curiosity comes in; hopefully here in bit when ur asked to walk 10 miles you can be ready for some more.