What is the equivalent rank of O-4 in the Marine Corps?

The equivalent rank of O-4 in the Marine Corps is Major. In the United States Armed Forces, ranks are categorized into pay grades, with O being the officer category. O-4 specifically corresponds to the rank of Major in the Marine Corps, which is a field grade officer rank. Officers at this level typically hold positions of increased responsibility and leadership, such as commanding a company or serving as staff officers at various levels of command.

To contextualize this within the Marine Corps rank structure, the progression moves from Second Lieutenant (O-1) to Lieutenant (O-2), then to Captain (O-3), with Major being the next step at O-4. Following Major is Lieutenant Colonel at O-5, showing a clear hierarchy in the officer ranks. Understanding these ranks and their equivalents across different branches of the military is essential for effective communication and operation within joint forces.