MS Bluefort was an accommodation vessel owned by the Canadian-based company Bridgemans Services Group LP. She was built in 1979 as a car/passenger ferry by Meyer Werft, Papenburg, Germany as Diana II av Slite for Rederi AB Slite for use in Viking Line's traffic. She has also sailed under the names Diana II, Vironia, Mare Balticum, Meloodia and ARV 1.

Rederi AB Slite had great success with their first generation of car and passenger ferries servicing between Sweden and Finland and by the late 1970s the growing market demanded larger ships. Slite's first route within the Viking Line marketing company had been that between Kapellskär and Naantali but this route had since been clogged with Viking Line ships and received competition from Silja Line's similar service between Norrtälje and Turku.

As a first step to find new markets, Rederi AB Slite had sold their merely six years old Apollo in 1976 and replaced her with the older Apollo III, making 24-hour cruises between Stockholm and Mariehamn. The company still served the Kapellskär—Naantali route with their other ship, the 1972-built Diana. But with four other Viking Line ships competing for the same cars and passengers on that route, Slite still needed to break new grounds to keep themselves profitable.

In 1974, the two other Viking Line partners started operating the Stockholm—Turku route which proved to be quite profitable. In preparation for the new ten-year agreement of collaboration between the Viking Line partners to be settled in 1980, Slite made the decision to try to push out Rederi Ab Sally from the Stockholm—Turku route with a newbuilding that would outmatch their current ship there, the Viking 4.

The new ship was planned together with her contracted builders, Meyer Werft, Papenburg in West Germany. This shipyard had built the Apollo and the Diana for Slite as well as four sister vessels for Rederi Ab Sally. The design greatly resembled the former ships but the newbuilding was larger in every respect. Among the distinguishing differences were the addition of a second car deck as well as a larger number of berths. The new ship was named M/S Diana II af Slite and launching took place on March 31, 1979.

Less than three months after her launch, the ship was delivered to Rederi AB Slite. On June 14, 1979, she was put into Viking Line service between Stockholm and Turku with daytime callings at Mariehamn, replacing the Viking 4. In September the same year, her registered name was shortened to Diana II, although this had been her marketing name since her delivery.

At the beginning of the summer season 1981, Diana II was transferred to the Kapellskär-Naantali route. Although she returned on the Stockholm-Turku during the summer of 1982, the Diana II remained on the Kapellskär-Naantali route for the rest of her Viking Line career.

During her time in Viking Line service, the Diana II encountered one serious incident. On February 5, 1989, she touched ground near Kapellskär and started taking in water. Due to her pumping system at the time only operated at half of its capacity, the ship took in a substantial amount of water and partially sunk in the shallow harbour of Kapellskär. She was soon refloated however and was docked for repairs.