The fortress was expanded in 1687 until 1689 to include three canon batteries and a blockhouse. The fortress served as an important base for Norwegian naval hero Tordenskiold and his fleet during the Great Northern War’s final Norwegian phase from 1709 until 1720 and as a central staging point for sea commerce from Denmark in this period. The fort was the homeport for the Danish-Norwegian Kattegat squadron. And not least, it served as a major chandelling and forwarding center for canon from the Norwegian ironworks and other equipment.
Fredriksvern and Fredriksvern Verft was established as the headquarters for the Norwegian Fleet from 1750 until 1758 so that the older fortification became part of the naval base. The oldest constructed building, ‘’Krutttårnet’’, has a distinctive architecture and today is a well known tourist attraction.