OCS is for those who have not had military indoctrination from NROTC or the Academy. (A few years ago, Aviation OCS was in Newport, it has now been combined with regular OCS and moved to Pensacola). Although the discipline taught at OCS is undoubtably important, one of the reasons for the length of OCS is the curriculum in Naval Science. NROTC candidates already receive this training, although some attend the much shorter (6.5 week) NSI, or Naval Science Istitute, in Connecticut to make up for anything they missed by not attending NROTC during Freshman and/or Sophomore years. This is different from OIS, or Officer Indoctrination School, the 6 week school for staff officers that covers more of how to wear the uniform and march along with some very basic military indoctrination. How do you know the difference? Officers at OIS are already commissioned.
From: http://www.catalogs.umn.edu/ug/rotc/rotc02.html
Naval Science Institute (NSI)—Students selected for either of the two-year programs attend the Naval Science Institute (NSI) in Newport, Rhode Island, following their sophomore year. NSI provides a six-week course of instruction in naval science and professional training. While at NSI, students receive pay, uniforms, room and board, and transportation. Successful completion of NSI qualifies students to enroll in the NROTC advanced course.
Curriculum
The naval science curriculum covers basic seamanship to fleet operations and provides intensive education in the art and science of being a naval officer. All midshipmen learn about the background and meaning of our national and naval traditions and the importance of professional and ethical performance. This awareness, combined with the opportunity to develop and practice basic leadership principles, affords them the inner confidence necessary to effectively lead others and assume the responsibilities of a Navy or Marine Corps officer.
Midshipmen take the course sequence described below. During the second and third years, they take either the Navy or Marine Corps sequence. In addition to the specified courses, students attend NROTC professional training for three hours each week. During the junior and senior years, these sessions emphasize command and leadership skills. NROTC students must also take certain University courses specified by the Navy.
Navy Sequence—First Year
Nav 1000—Professional Training in Naval Science
Nav 1101—Introduction to Naval Science
Nav 1102—Seapower and Maritime Affairs
Navy Sequence—Second Year
Nav 2000—Professional Training in Naval Science
Nav 2201—Ship Systems I (Naval Engineering)
Nav 4401—Leadership and Management I
Navy Sequence—Third Year
Nav 3000—Professional Training in Naval Science
Nav 3301—Navigation I (Piloting and Celestial Navigation)
Nav 3302—Navigation II (Seamanship and Ship Operations)
Navy Sequence—Fourth Year
Nav 4000—Professional Training in Naval Science
Nav 2202—Ship Systems II (Weapons)
Nav 4402—Leadership, Management, and Ethics II
Marine Option—Second Year
Nav 2000—Professional Training in Naval Science
Nav 3310—Evolution of Warfare (can also be taken in third year)
Marine Option—Third Year
Nav 3000—Professional Training in Naval Science Nav 4410—Amphibious Warfare (can also be taken in fourth year)
Students register for NROTC courses in the same manner as for other courses in their academic programs. These courses carry academic credit and may be used to fulfill University degree requirements. Students who are not in the NROTC program may enroll in a naval science course as an elective with the instructor's consent.
https://www.cnet.navy.mil/netc/ois/
Director's Welcome
"On behalf of the staff of Officer Indoctrination School (OIS), I congratulate you on your choice to become a United States Naval Officer. To prepare you for this new role, you will attend our six-week indoctrination program located at the Naval Education and Training Center (NETC), Newport, Rhode Island. Our mission is to prepare newly commissioned officers of the Medical Corps, Dental Corps, Nurse Corps, Medical Service Corps, Judge Advocate General Corps, and selected Nuclear power specialists to carry out the duties and responsibilities of a naval officer. Our training vision is to incorporate and actively practice the Chief of Naval Operation's vision of operational primacy, leadership, teamwork, and pride into every facet of our indoctrination program. Our administrative vision is to graduate all students on time and with no unresolved administrative issues. Through continuous process improvement, we assess the way we do business to provide the best possible product to our customers. There is quite a bit of information contained in this web site to help you prepare for OIS and I encourage you to read it thoroughly. My superb staff of officers, enlisted, and civilian personnel and I look forward to your arrival and especially to the opportunity to be a part of your new adventure."