The Flyvefisken ships were constructed using an innovative modular design known as StanFlex: they have a standard hull in which containerised weapons or systems can be placed.

Furthermore the ships are built using the sandwich principle - a layer of fiberglass either side of a core of PVC cell foam.

Four vessels of the class (Glenten, Ravnen, Skaden and Viben) were acquired by the Portuguese Navy in 2010 and re-named Mondego, Douro, Guadiana and Tejo.

After a period of upgrade and reconfiguration, Mondego and Tejo were specifically tasked to police Portugal's exclusive economic zone around Madeira.

The navy rejected the claim, which was made after the vessel had been tasked to monitor a Russian ship sailing in the vicinity of Madeira.