Which of the following ranks is not among O-9?

The rank that is not among O-9 is Rear Admiral (Lower Half). The O-9 classification refers to the higher echelons of military ranks, specifically the ranks of Vice Admiral in the Navy and Lieutenant General in the Army, Air Force, and Marine Corps. These ranks fall under the O-9 pay grade, reflecting their senior leadership positions.

On the other hand, Rear Admiral (Lower Half) is categorized as an O-8 rank. This means that while it is a senior rank, it does not reach the level of O-9. Therefore, it is important to distinguish the ranks based on their specific classifications and pay grades to understand the hierarchy within military structures. Brigadier General also falls under the O-7 category, and Rear Admiral (Upper Half) is classified as O-9, reinforcing the understanding that only those ranks recognized as O-9 can be grouped in that category.