Prior to World War I, Marine officers came primarily from the Naval Academy or were commissioned from the enlisted ranks.

OCS screens potential officers using a program designed to test and assess the candidates by using the three graded categories of Academics, Leadership, and Physical Fitness.

Candidates must maintain a minimum of 80% in Academics, Leadership, and Physical Fitness to graduate, as well as passing all the mandatory pass/fail events such as the Endurance Course.

Academic subjects covered include Marine Corps history, leadership, close order drill, weapons handling, and general military subjects such as land navigation, the Uniform Code of Military Justice, interior guard, moral and ethical leadership, and basic combat.

Physical training, small unit leadership, and basic infantry tactics are addressed, as well as significant academic instruction.

PLC Seniors is an advanced course of indoctrination and contains similar physical training, small unit leadership, infantry tactics, and academics; but at a faster rate and with more instructor-induced stress.

The main alternative is the Officer Candidates Course, which is designed for college seniors or graduates and enlisted Marines, and consists of one ten-week training session.

While the curriculum is identical to the 10-week PLC Combined session, OCC is held three times a year (winter, summer, and fall), and accepts only college graduates.

It consists of a long canal with 4-foot (1.2 m) cement culverts submerged in swampy water; candidates must immerse themselves and navigate through the Quigley without standing as a part of the OCS training program.

Midshipmen also learn basic military skills such as land navigation, combat orders, offensive combat tactics, and basic weapons familiarization, which are applied during multi-day field exercises including the culminating event when each midshipman is given the opportunity to lead a squad attack on an objective.

This article incorporates public domain material from websites or documents of the United States Marine Corps.