The second structure was built on the same site by Robert Mylne under Charles II's order at the beginning of the Second Anglo-Dutch War in 1665, at the cost of 28,000 £. It stopped a Dutch fleet in 1667, believing that its manned and firing capacity was much higher than the actual situation. In fact, the walls have not been completed, and there are few guns. At the end of the war, the government decided not to garrison Lerwick, making the war trivial; during the Third Anglo-Dutch War in 1673, when the Dutch burned it down, it was left unguarded.
It was rebuilt in its current form in 1781 and named after George III's wife but has never served in hostilities since. It was stationed during the Napoleonic Wars and later became the base of the Royal Naval Reserve. From 1837 to 1975, it was used as a prison and court in the town and later as a customs and coast guard.