First -- My going-in point -- Congress establishes how many people may be on Active Duty at any one time, within each of the Services. Then the Services (Army, Navy, Marines, Air Force) arefunded to support that many people. Sounds easy, yes? You hire to fill vacancies; and you plan attrition. Actually, not so ...
Suffice to say, the USAF just announced a new round of "force shaping" initiatives which will impact both officers and enlisted, and target folks with: (1) less than 6 years time in service, (2) 6-12 years time in service, and Lt Col's and Col's who are over 20 years of service. Now before you grab the paper bag and practice your breathing drills, you need to check some of the data to see if your or a friend's spouse is in the target (poor choice of words) audience.
Want to know more? Check this link from the Air Force Personnel Center. Force Management Options
Know your options; plan your lives; keep both eyes wide open. Over & Out, MaintenanceToadOne