Which rank is identified as O-4?

The rank identified as O-4 is Commander. In military ranking systems, specifically within the United States Navy and other branches where similar rank structures exist, the "O" designator refers to officer ranks. The rank of Commander is classified as O-4, which places it in the middle of the officer ranks above Lieutenant Commander (O-3) and below Captain (O-5).

The reason Commander is O-4 is based on the standard progression of naval ranks, where each rank designates a specific level of authority, responsibility, and years of experience. Commanders typically oversee significant departments or units and have a critical role in operational and administrative functions.

Other ranks mentioned, such as Lieutenant Commander (which is O-3) and Captain (which is O-6), represent different levels of seniority and responsibility, helping to establish a structured hierarchy within the military.