I'm often asked if one can really get a college degree while on active duty. The answer is yes. Several hundred enlisted military personnel do this every year.
Each military base has an Education Office, who have arranged for colleges and universities to conduct college courses on-base, leading to various degree programs. However, one should realize that it takes much more time, then if you were going to college full-time as a civilian. For the most part, you're taking college courses, part-time, while off-duty on the weekends and evenings. Additionally, what your job is, and where you are assigned will play a large part in determining how much "free time" you have to attend college courses. A finance clerk assigned to a squadron that rarely deploys will have a better opportunity to attend off-duty college courses than an infantry troop, assigned to a company that trains "in the field" often.
However, even for those who don't work a "regular schedule," distance-learning has changed the face of getting an off-duty education. There are now several universities (some associated with the military, some not) who will allow you to take most (if not all) courses via the Internet. The Army even has a program where they will issue a free laptop computer to recruits enrolled in authorized distant learning programs. The Navy takes college professors with them on some of their larger ships, so they can offer off-duty college courses to sailors at sea.
In addition to taking courses off duty, each of the services have programs which allow some enlisted to remain on active duty and attend college full-time (receiving full pay and allowances). Some of these programs lead to a commission as an officer, some do not. Most require that you commit yourself for a longer hitch in the military. Most require that you obtain some college (usually two or three years) on your own, first. ALL of these programs are extremely competitive. There are many, many, many more applicants for these programs than there are available "slots" each year. So, if you plan to compete for one of those few available slots, you need to be the "best of the best." That means top grades, outstanding military record, and "walk on water" written recommendations from your supervisors and commander. For details, see our Education & Training Resources.
Enlisted members who do obtain a college degree while on active duty can apply for a commission through Officers Candidate School (Officer Training School for the Air Force). Again, there are generally many more applicants each year then there are available "slots," so -- if you want to be selected -- you have to be among the top.
The Army and the Coast Guard are the only services in which an enlisted member can obtain a commission without having a 4-year college degree. Enlisted members in the Army can attend OCS and be commissioned with only 90 college credits. However, they must complete their degree within one year of being commissioned, or they risk being reverted (rifted) to their previous enlisted rank. See Army Officer Candidate School (OCS) for more information.