First Duty Assignments
There are only two services that will guarantee (in the enlistment contract) a specific first duty station. For details, see Part 4 of this series.
Note: The Guard and Reserves also guarantee the duty station because they are recruiting to fill specific, open slots in specific Guard & Reserve units.
For everyone else, first duty station selection is made (in either basic training or technical school/AIT/A-School), based upon your preferences, and the "needs of the service." In most cases, you fill out a form, known as a "dream sheet" to list your assignment preferences. While the services will consider your preferences, the overriding deciding factor is where the military needs you the most. If that coincides with one of your preferences, great. If not, you'll be assigned to where the service wants you.
For the most part, for the first duty assignment, the "dream sheet" is best thought of as a tie-breaker. For example, let's say the service needs you equally bad at base X and base Y. They now have to decide which of these two bases will get the pleasure of your company for the forseeable future. They look at your dream sheet and see you have base Y listed as one of your preferences. Problem solved! You'll be assigned to base Y! On the other hand, assume you have base Z on your dream sheet, but the service needs people the most at base X and base Y. You ain't gonna get base Z. The service will be assigning you to either base X or base Y, regardless of what is on your assignment dream sheet.
For some Navy Jobs, your assignment can also be based on your class-standing in "A-School." In other words, the person at the "top of the class," would have a better chance of receiving the assignment he/she wants than the person at the "bottom of the class."
Of course, it goes without saying that assignments are based on valid vacancies. If you have the job of "tank-fixer," you're only going to be assigned to bases that have tanks to fix.
After the first duty assignment, assignments are done a little differently. In most cases, you'll have a little more say in future assignments, than you have for the first duty assignment. There are a few restrictions, however:
First-term (those in their first enlistment) enlisted members assigned to a CONUS (stateside) location must have 12 months time-on-station before being eligible to move to an overseas location, and must have 24 months time-on-station before being allowed to move to another CONUS location.
Career (those who have re-enlisted at least once) enlisted members assigned to the CONUS must have 24 months time-on-station to move to an overseas location and must have 36 months time-on-station in order to move to another CONUS location.
Truth be told, the miltiary services are doing fewer and fewer CONUS to CONUS moves. For all practical purposes, if you are assigned to a CONUS base, and you want to move, you're going to have to volunteer for an overseas tour (or sea duty for Navy).
The length of time one spends on an overseas tour depends on the location. For example, most of Europe and Japan are considered "standard" overseas tours. The length of the assignment is 24 months for single people, or those with dependents who elect not to bring their dependents, and 36 months for those who bring their dependents. Another type overseas assignment, like most assignments to Korea are considered "remote." On a remote tour one cannot bring their family at government expense, and the tour-length is 12 months. On the other hand, those returning from a remote tour usually get assignment preference over those returning from a standard tour.
In most cases, if you are at CONUS base X, and you hate it there, the only way to move to a different CONUS base is to volunteer for an overseas assignment, then hope you get a CONUS base you like when you are reassigned back to the CONUS, following the overseas tour.
For "standard" overseas tours, one can generally increase their chances of being selected by volunteering for the "Extended" tour length. This is the standard tour, plus 12 months. For example, let's say that there is one vacancy in Germany for a person in the paygrade of E-5, with the MOS (job) of XXX. There are two E-5s with MOS XXX who have volunteed for Germany. One of them volunteers for the "standard" tour, which is 24 months with no dependents or 36 months with dependents. The other volunteers for the "Extended" tour length, which is the standard tour, plus 12 months. The E-5 who volunteered for the extended length will get the assignment, because staying there an extra year will save the military money.