What is the title of the type of Admiral that can be promoted during wartime?

The title of Fleet Admiral is specific to the United States Navy and refers to a rank that can only be appointed during wartime or in other exceptional circumstances. This four-star rank is the highest possible in the naval hierarchy and has been designated to only a few individuals in history, primarily during major conflicts. The position was established to provide a single officer with command over all naval forces during warfare, ensuring clear leadership and strategic coordination across the fleet.

In contrast, the other ranks mentioned, such as Admiral, Vice Admiral, and Rear Admiral Upper Half, are significant but do not carry the same wartime stipulation. These ranks can be attained during peacetime and are part of a regular command structure. Therefore, Fleet Admiral stands out as the title associated with promotion specifically in the context of wartime.