The general overhaul and upgrade work on the submarine was carried out by Saab Kockums as part of a contract awarded to the company on 29 September 2014.
The enhancements provided include new sensors and navigation systems. The company has also implemented the required assessments to assure the submarine’s operational availability.
Saab Kockums is set to carry out a mid-time upgrade for another Gotland-class submarine in the near future.
Saab Kockums head Gunnar Wieslander said: "Modification of submarines is our daily business. We are continuously working with upgrades of the existing submarine fleet. At the same time, Saab Kockums is now building the A26 next-generation submarine for the Swedish Navy.
"It is a 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."
Sweden’s three Gotland-class vessels, HMS Gotland, HMS Halland and HMS Uppland, were commissioned in the late 1990s.
Last year, FMV awarded a $17.9m contract to Saab to carry out refurbishments on HMS Halland.
HMS Halland conducted training in the Mediterranean in the year 2000, along with the French, Spanish and the US Navies, while HMS Gotland was based in San Diego, California, for two years (2005-2007) to participate in training with the US Navy.