The different services have slightly different procedures, but generally they all work like this...

ROTC scholarship students have higher odds of active duty and getting their choice of assignment. ROTC participants who are not on scholarship have lower odds, but it all depends on requirements at the time.

Generally, job asignments are based on merit, using screening boards and/or interview(s). The ROTC students get to submit a dreamsheet indicating their preference.

For any job, selection is based first on the needs of the service, then on merit, and lastly on random luck. In order to maximize your chances for a certain job...

1) Be fully medically qualified. You might be able to get a waiver for certain things, but that will probably make you less competetive than those who are qualified. About the only control you have over this is to stay in shape, consider laser-vision surgery, and avoid motorcycles.

2) Be physically qualified. Stay in shape. Maintain good run, swim, and calesthentic numbers.

3) Get good grades. This will be the largest competetive factor, both for your job assignment and for future civilian educational opportunities...you only get one chance at this, don't blow it.

4) Participate in ROTC operations, and don't screw off. Play their game... this is not as important as grades, but still counts.

5) Participate in military-sponsored civilian flight training, if offered. If your service does not provide any, do some civilian flight training...try to get a PPL and maybe an IRA.

Note: The navy, usmc, and uscg have a lot of helicopters. Nothing from your college background will prevent you from being assigned to helicopters once you get to flight school. If you want to be an airline pilot, this will not be good.