Early Swedish kings ( 9th–14th centuries) organised a Swedish Navy along the coastline through "ledungen". This involved combined rowing and sailing ships (without artillery). This system became obsolete with the development of society and changes in military technology. No later than in the 14th century, the duty to serve in "ledungen" was replaced by a tax. In 1427, when Sweden was still part of the Kalmar Union (with Denmark and Norway), Swedish warships did however participate in the naval battle of Öresund against the Hanseatic League. It is unclear how this force was organised and exactly on what basis.