In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.

Passage: The town was built on the mouth of a small tributary of the Severn Estuary near the mouth of the River Avon. The old pill or jetty provided protection for craft against the Bristol Channel's large tidal range, and iron rings can be seen in the high street at which fishing boats used to moor. Its position meant Portishead was used to guard the "King Road", as the waters around the headland are called. In 1497 it was the departure point for John Cabot on the Matthew. A fort was built on Battery Point, and was used during the English Civil War when the town supported the Royalists, but surrendered to Fairfax in 1645. Guns were also placed at Battery Point during World War II. The King Road was the site of a naval action in 1758 when HMS Antelope captured HMS Belliqueux, one of a French squadron returning from Quebec.
Link Information: A fort was built on Battery Point, and was used during the English Civil War when the town supported the Royalists, but surrendered to Fairfax in 1645. Answer: 3
How long had the English Civil War been going on for when the fort at Battery Point surrendered to Fairfax?