The American armed forces are going through a massive reorganization, an undertaking that tends to get overlooked because theres a war going on. As a result of the new tactics and organizations, a lost of military people have been persuaded to train for new jobs. But there is resistance. 

Many civilians still think that, when you join the military, you are assigned whatever job the service needs you to do, rather than what you might want to do. That was true during World War II, and for draftees for as long as the peacetime draft lasted (until 1972.) But once the armed forces became all volunteer, the military had to pay more attention to what recruits wanted to do, in order to get people to sign up. Potential recruits are given aptitude tests, and then told what jobs they are qualified for, and offered ones in areas that had the most shortages. Frequently, the potential recruit couldnt get the job they wanted, and walked away. Successful recruiters tend to be very good at convincing young people to take jobs they never thought of taking.

The current reorganization came about because the military has to deal with the Cold War being over, and a lot of new technologies are now available that change the way wars are fought. Oh, and theres the war on terror as well. For the air force and navy, a lot of the new technology has meant they dont need as many people. Being able to downsize made it easier for the air force and navy to convince their people to switch jobs (and go through weeks or months of retraining.) Typically, the offer to switch was made when re-enlistment time came. If a switch was not accepted, re-enlistment was not allowed. Sort of, an offer you cant refuse type situation. Actually, the air force and navy got more than enough volunteers to switch, and now has to lay off thousands of airmen and sailors they simply don't need. 

The army situation was different, because soldiers are currently doing most of the heavy lifting in the war on terror. The army doesnt want to lose anyone just because they wont volunteer to switch careers. But it turns out that army regulations allow for Involuntary Classification, meaning a soldier can be ordered to switch to a new job. This authority is rarely used these days, and the last time was about twenty years ago. The army is proceeding carefully, and has only sent out 140 Involuntary Classification notices so far. The army does not want to lose good people, but it also cannot afford to have people doing jobs that are no longer needed. The idea is that most of the people ordered to switch will be satisfied with, or adapt to, the new job and stay in the service.