The Norwegian Defense Materiel Agency has awarded Kongsberg Defense with a $36 million contract to upgrade Fridtjof Nasen-class frigates.

The upgrades for the vessels will include the combat management and active sonar systems. The company has previously supplied anti-surface and anti-submarine warfare systems based on the integrated Aegis Combat System. Officials estimate the work will be complete after four years, and will effectively extend the service life for the ships.

"Kongsberg is pleased to be part of the upgrade program extending the lifetime of the systems on board the Fridtjof Nansen class," Kongsberg Defense acting president Eirik Lie said in a press release. "Kongsberg is a leading Combat System supplier for ships and submarines delivered to eleven nations around the world, and this contract confirms our strong position."

Fridtjof Nasen-class frigates are the primary maritime surface combat units for the Royal Norwegian Navy, and take their names from famous Norwegian explorers. The vessels are manufactured by Spanish shipbuilder Navantia.

The ships are designed to meet a variety of threats including submarines and attack aircraft, and are typically armed with Evolved Sea Sparrow missiles, Sting Ray torpedoes, and an OTO Melara cannon.