In the military structure, what is the designation for a rank of O-4?

The rank designation of O-4 corresponds to a Lieutenant Commander in the military structure. This rank is typically found in the Navy and Coast Guard, where it falls above that of a Lieutenant (O-3) and below a Commander (O-5). The Lieutenant Commander holds significant responsibility and often commands smaller vessels or serves as department heads on larger ships, as well as in various staff roles.

The other ranks listed do not correspond to O-4. The Lieutenant Junior Grade is an O-2 rank, the Senior Chief Petty Officer is an E-8 rank in the enlisted ranks, and the Warrant Officer, depending on the service branch, generally corresponds to a rank of O-1 or O-2. Understanding these distinctions is crucial for recognizing the hierarchy and roles within military ranks.