Just as many political and military doubts there were about the ground defence line, everybody agreed in the necessity of a naval defence line. The experience from 1802 and 1807, where Copenhagen was forced to surrender from the seaside, made it clear that this was the weak point of the city and the country.
There were an inner line of the three old forts and batteries:
Furthermore three new constructions were made in mid 19th century:
The Coastal Battery “Kalkbränderi Battery” (demolished)
The Naval Fort”Mellemfort” (demolished)
The Naval Fort “Prövestenen” (exist, but access is very limited.)