Final answer:
The rank just below Captain in Britain's Royal Navy is Commander. This ranking is part of a hierarchy that includes other ranks; Admiral is higher while Lieutenant and Ensign are lower.
Step-by-step explanation:
In Britain's Royal Navy, the rank just below captain is Commander. The hierarchy of naval ranks places each rank in a specific order, with Admiral actually being higher than Captain, and ranks such as Lieutenant and Ensign being lower. As an example of naval hierarchy, Admiral Chester Nimitz, who was a Commander of the US Pacific fleet during World War II, was promoted to the highest-ranking officer of the navy, Fleet Admiral. Admiral Nimitz is famously known for accepting the surrender of Japanese forces aboard the USS Missouri at the end of World War II.