British preemptively captured large portions of the Danish naval fleet to prevent the French from doing the same. As a result, the Danish government declared war and built small gunboats in large numbers to attack the British. The Gunboat War (1807�1814) was the title given to naval conflict between Denmark-Norway against the British navy. It was natural for Flekkefjord to move from a smuggler's haven to blockade runner's headquarters. The unusual tides there were unknown to the British warships that were blockading the Norwegian coast against Napoleon-supporting ships and this provided the blockade runners a considerable advantage.
After the war the Dutch maintained a strong presence in Flekkefjord, and continued exporting oak and pine. The pine was used mainly to make foundations for the boom in Amsterdam house construction; as a result most of Amsterdam�s houses from the 19th century are constructed of pines from Flekkefjord exporters. A section of Flekkefjord called �Hollenderbyen� (town of the Dutch) dates from the 18th century.
Xenotime, a rare yttrium phosphate mineral whose chemical formula is YPO4, was discovered in 1832 at Hidra (Hitter�), Flekkefjord.
The herring fisheries deserted the coast in 1838, depriving Flekkefjord residents of their main export. Tanning replaced fishing and by 1866 five tanneries were operating in Flekkefjord.
The Flekkefjord Line railway ran between Sira and Flekkefjord from 1904 to 1990
