This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.

Passage: Once known as "the Gibraltar of the West" and "Fortress Bermuda", Bermuda today is defended by forces of the British government. For the first two centuries of settlement, the most potent armed force operating from Bermuda was its merchant shipping fleet, which turned to privateering at every opportunity. The Bermuda government maintained a local militia. After the American Revolutionary War, Bermuda was established as the Western Atlantic headquarters of the Royal Navy. Once the Royal Navy established a base and dockyard defended by regular soldiers, however, the militias were disbanded following the War of 1812. At the end of the 19th century, the colony raised volunteer units to form a reserve for the military garrison.
What was known as the Fortress of the West and Gibraltar Bermuda?