Both when the Naval base was first established and for many years thereafter, the construction of a network of fortifications was carried out on Trossö, the neighbouring islands and on the inner and Outer western and eastern roadsteads.

In 1680, in compliance with Erik Dahlberg’s proposals for the defence of the main fairway into Karlskrona, work was begun on the Drottningskär citadel and the Kungsholm fortress. At first Drottingskär was the principal stronghold, but in the beginning of the nineteenth century this responsibility was assumed by the Kungsholm fortress. The fortified towers of Kurrholmen and Godnatt on islets further up the fairway are also from the eighteenth century whilst the fortifications nearest the town, Koholmen, Mölnarholmen and Ljungskär, date from the seventeenth century.

From the beginning it had been proposed that the harbour and dockyard should be protected from attack from both land and sea by a girdle of fortifications.