Which officer rank is O-3 in the Marine Corps?

In the United States Marine Corps, the officer rank designated as O-3 is Captain. This rank follows O-2, which is First Lieutenant, and comes before O-4, which is Major. A Captain typically has responsibilities that include leading a company-sized unit, overseeing operational planning, and managing personnel matters within their command. Understanding the ranking structure is essential for effective communication and organization within military settings, as each rank carries specific authority and responsibilities.