What rank is O-3 in the Marine Corps?

The rank O-3 in the Marine Corps is properly identified as Captain. In the military ranking system, the designation "O" stands for "officer," and the number represents the pay grade. Therefore, O-3 is the third pay grade for commissioned officers, which aligns with the rank of Captain. Captains typically serve in leadership positions overseeing units, and they are often responsible for managing a platoon or a similar-sized organization.

The other ranks listed—Major, First Lieutenant, and Lieutenant Colonel—correspond to different pay grades (O-4, O-2, and O-5, respectively) within the Marine Corps hierarchy. Each of these ranks has its own responsibilities and authority levels, distinct from those of a Captain. Understanding the structure and responsibilities associated with each rank helps clarify the correct answer further.