Denmark, Iceland and Norway are already members of NATO and played a pivotal role in founding the alliance.
The first NATO nations signed the North Atlantic Treaty setting up the organisation in 1949.
Among those signing the treaty on April 4 that year were Western Union members France, the UK and their Benelux allies, the US, Canada, Portugal, Italy, and Nordics Denmark, Iceland and Norway.
Each of those Nordic nations joined with specific arrangements limiting their participation that remain in effect today.
source: express.co.uk