The rank of Admiral in the Navy is the highest rank. What is the next lowest rank?

The rank of Rear Admiral is indeed the next lowest rank below Admiral. In the United States Navy, the hierarchy of ranks places Admiral at the top of the scale, with Vice Admiral ranking just below it. The rank of Rear Admiral follows Vice Admiral and typically encompasses officers in command of larger naval units or significant naval operations.

To understand the context, Vice Admiral represents a three-star rank, while Rear Admiral is categorized as a two-star rank. This clearly establishes Rear Admiral as the immediate step down from the highest rank of Admiral. The ranks of Captain and Commander, while certainly significant positions within the Navy, fall even lower in the hierarchy compared to the Rear Admiral. Captain is usually a single-unity command rank, and Commander is a step below that. Therefore, Rear Admiral is demonstrably the next lowest rank after Admiral, making it the accurate answer.