The Baltic Islands in Sweden (Åland and Jutland) and in Denmark (Bornholm) have been demilitarized since 1856 following an agreement reached by Russia and the main European powers. After Finland's recent accession to NATO, it and Sweden and Denmark began procedures to militarize these islands.

The idea of turning the Baltic Sea into NATO's inner sea in the west has been lifted in 2018. Britain, Denmark and Norway have been involved in a program to equip their national navies with the U.S. Aegis combat information and control system.