What is the equivalent of O-10 in terms of rank?

The equivalent of O-10 in terms of rank is Admiral in the Navy or General in the Army, Air Force, or Marine Corps. The designation O-10 represents the highest ranks in these branches of the military.

Admiral and General carry the same significance across the services, indicating that they are the top operational leaders, responsible for large formations and organizations. Fleet Admiral is a special rank that is not regularly held and is considered a rank above O-10, specifically created only during times of war. Therefore, it does not apply in the context of standard rank equivalency. Rear Admiral (Upper Half) and Brigadier General are ranks that are below O-10, further confirming that the correct answer pertains to the highest level of officer rank represented by O-10.