What is the rank of an officer denoted by O5?

The rank denoted by O5 is Commander. In the United States Navy and other branches of service, officer ranks are categorized by a system that assigns codes for each rank, with 'O' designating officer ranks. The number following the 'O' indicates the relative seniority of the rank, with O1 being the lowest officer rank and increasing to higher ranks as the number increases.

Specifically, in the Navy, Commander (O5) is positioned above Lieutenant Commander (O4) and below Captain (O6). This rank typically involves more responsibility, usually commanding a medium-sized ship, a significant shore command, or serving in high-level staff positions.

The other options represent different ranks that do not correspond to O5. Captain (O6) is a rank above Commander, Rear Admiral Lower Half (O7) is a flag officer rank, and Lieutenant Colonel is used in the Marine Corps and the Army, which are not denoted by the O5 code.