Saab has redelivered one of the Swedish Navy's Gotland-class submarines following overhaul and upgrades.

Saab was contracted to perform the overhaul and upgrades to the vessel in September 2014. The upgrades include new sensors and navigation systems. The company says another of the three Gotland-class submarines will also undergo upgrades and maintenance.

"Modification of submarines is our daily business," Saab Kockums business unit head Gunnar Wieslander said. "We are continuously working with upgrades of the existing submarine fleet."

The Swedish Navy's Goltand-class fleet includes the HMS Gotland, HMS Halland, and HMS Uppland, all commissioned in the 1990s. The submarines, manufactured by Saab Kockums, are designed for anti-ship warfare, surveillance, special operations and mine-laying tasks. The Gotland class was the first submarine class in the world to operate with an air independent propulsion system.

The vessels are regularly used for training exercises with the U.S. Navy.

"It is future-proofed vessel with a design that allows for faster and easier upgrades. Everything we do is driven by the need to make our submarines as modern and effective as possible," Wieslander added.