From an Air Force perspective, it is very competitive to match seeing how we only have 4 military spots at Wilford Hall. But, for any of the branches, it is true that the level of competition varies each year based on 1) number of applicants 2) number of available spots, including civilian deferments. The PD for the AF told me that even if he had more spots than applicants, if the applicant was not "ortho quality" than, he would not rank him for either civilian or military ortho spot. Bottomline, you may be able to slide into a military ortho spot...but you have to meet a minimum criteria.
Also, in the military match, a point system is in place where 4th year students are at the bottom of the totem pole and years in service carries the weight. So, you can be an all-star 4th year applicant...but you will lose out to a average Captain with time as a flight surgeon. So, if you have 4 flight surgeons or Captains applying against you, you're not in a good spot unless one of them is not "ortho caliber" in general.
The tips are to ROTATE at the location you want to get into. In the AF it's easy cause there is only one spot. Do all of the things you would normally do to ace a rotation (work hard, be cordial, do extra work, etc). Work with as many attendings as you can to spread your name. I know that resident feedback is huge as well. As for rotating at other air force bases, not ortho, you can definitely make connections cause AF medicine is small, AF ortho is even smaller. I did 2 ADTs, non-ortho, and spent time with the ortho guys post-call and they knew the higher ups at Lackland. So, always work hard and try to make connections here and there.
I'm a DO student too and was able to get a civilian deferment and matched. It's definitely possible, but my year they gave out a ridiculous 20 or so deferments.
Good luck.
CP