There are several different options to becoming an Army Officer through ROTC.
Four Year Option:
Enroll in the program as a freshman and complete four years of the program.
Two or Three Year Option:
Transfer in as a junior or a two-year graduate program and complete 2 years of the program as well as a summer Leadership Training Camp (LTC) to catch up on the other 2 years. LTC can be substituted for certain previous military experience.
Simultaneous Membership Program (SMP):
The Simultaneous Membership Program allows you to attend Army ROTC and serve in the U.S.Army Reserve or Army National Guard at the same time. It gives you an opportunity for additional training and experience. Cadets serve as Officer trainees in the Reserve or National Guard while completing college. You can earn Reserve/Guard pay and benefits in addition to your Army ROTC allowances.
Prior to completing the ROTC program, you must select which branch of the army you want to be in. You can choose between active duty, reserve, or national guard.
What is the difference between someone who is active duty military and someone who is in the Reserve or National Guard?
Active Duty
A person who is active duty is in the military full time. They work for the military full time, may live on a military base, and can be deployed at any time. Persons in the Reserve or National Guard are not full-time active duty military personnel, although they can be deployed at any time should the need arise.
The Reserve
Each branch of the military has a Reserve component and the Reserve are under the command of their respective military branch (e.g., Army Reserve are under the command of the Army). The purpose of the Reserve is to provide and maintain trained units and qualified persons to be available for active duty in the armed forces when needed. This may be in times of war, in a national emergency, or as the need occurs based on threats to national security. Their presence can be called upon to serve either stateside or overseas. The primary job of the Reserve is to fill the gaps in stateside service positions when the active duty forces ship overseas. Members of the Reserve are required to participate in training drills one weekend a month and two weeks per year. Reservists generally deploy as individuals supporting a unit or in small groups.
National Guard
The National Guard consists of the Army National Guard and the Air Force's Air National Guard. While federally funded, the National Guard is organized and controlled by the state. However, in times of war, the National Guard can become federalized and deployed. The National Guard engages in a number of activities. During local emergencies, National Guard units assist communities endangered by storms, floods, fires, and other disasters. National Guard companies deployed overseas may see combat but are more often building schools and hospitals, training local peacekeepers, or teaching local farmers more efficient farming techniques and better ways to use of their land. As with the Reserve, the National Guard requires training drills one weekend a month and two weeks per year. National Guard members are given Veteran status if they have served for 30 consecutive days in a war zone. The National Guard deploys as a large unit so that they stay with the people they have trained up with.
Once your branch has been chosen you will take the oath of office and commission into that branch upon completion of the program.