Surprisingly there are quite a large amount of ways to become an Officer in the Army and many (if not all) of these routes apply to most of the other branches. No matter what the commissioning source is, officers are required to attend a branch specific Basic Officer Leadership Course (BOLC) that will teach them the specificities of their branch. Make sure you pick up a copy of the Army Officer’s Guide
OCS: OCS stands for Officer Candidate School and is the most used method for prior service military (enlisted Soldiers that want to become an officer), however you do not need to be prior service to go to OCS. If you are a civilian going into OCS you will need a bachelors degree and you will also be required to pass basic training as a requirement. If you are prior service you will need at least 90 credit hours of college to be accepted into OCS. You will be expected to finish your degree by the time you hit Captain. In recent years OCS has become extremely competitive and entry Army Physical Fitness Test (APFT) scores for an OCS slot have been 270 or greater. If your PT score is too low to be accepted you can expect to wait until the next OCS class starts. If you do not get accepted to that class you may be kicked out of the program. OCS is located at Ft. Benning, Georgia and at the time of this writing was 12 weeks of classroom, field training exercises, basic leadership and, Soldiering tasks. All events and test will be scored, and your class’ aggregate scores will be composed into an Order of Merit List (OML) which will rank you among your classmates. The reason why the OML is so important is you will pick your branch (what you will do in the Army) according to the OML. OCS commissions around 1,000 second lieutenants each year. OCS graduates will generally incur a minimum of a 3 year service obligation.
ROTC: ROTC stands for Reserve Officers’ Training Corps. This is the most common form of commissioning and is mostly used by civilians with no prior military service. It is however also open to prior service Soldiers, and many do utilize this option. There are more than 270 ROTC programs at most major universities in every state. In your state, there will be an ROTC program. In essence ROTC allows you to train to be an Army officer while you get your degree. After you graduate from your university and ROTC you will be a second lieutenant. Most people wishing to commission in the US Army will do so with ROTC because it is generally more accessible than the other commissioning sources. The Army will generally assign your branch based on the Army’s need, your degree and what your preferences are. Graduates of ROTC will incur a service obligation dependent on how much of your schooling the Army paid for.
United States Military Academy: Also known West point, it is generally considered the toughest commissioning sources, both in the competitiveness to get in, and the difficulty in graduating successfully. Based in West Point, New York this is a 4 year educational program that will give you a bachelors degree as well as a commission in the US Army when you are done that is fully funded by the Army in exchange for a service obligation. Similar to OCS, West Point only graduates about 1,000 commissioned officers every year. To get into West Point you will have to apply directly and have a nomination, typically from a Congressional representative. You do not need to know the representative, however the nomination process normally involves numerous letters of recommendation (teachers, business owners, etc.), written essays, and a formal interview. You are also required to be 17 to 23 years old, not married and no kids. In addition to that you will need high standardized test scores and strong grades. Prior service Soldiers are rare at West Point. Being extremely competitive, in 2012 the United States Military Academy had an acceptance rate of around 12%. If you want a guide on how to apply, prepare, and survive West Point, I would recommend The West Point Candidate Book
Direct Commission: This is typically reserved for civilians that have a unique set of skills that is mission critical for the success of the army. They do not need to go through the normal commissioning sources, but will typically have a degree of some sort. The people eligible for this are generally lawyers, dentists, doctors, nurses, engineers and chaplains. They will usually go through a 2 to 5 week military familiarization course which consists of military history, customs and courtesies and basic Soldiering skills.