In 1979 Mare Balticum was built by Meyer Werft  in Papenburg, Germany, for Rederi AB Slite to be used in Viking Line's traffic. She has also sailed under the names MS Diana II and MS Meloodia.

The vessel was ready on March 31, 1979 and got the name Diana II av Slite. The ship was meant to replace Rederi AB Slite’s previous ship, which was also named Diana that was built in 1972 and served until 1979 on the route Kapellskär–Naantali. "Slite" referred to the shipping company. Already in September of the same year the name was registered as Diana II – actually, this had been her marketing name since her delivery.

On June 14, 1979 she was put into Viking Line service between Stockholm and Turku, replacing the Viking 4 that belonged to the competing company Rederi AB Sally. The loss of the prestigious Stockholm—Turku route made Rederi AB Sally take action. After a record building time of 8 and a half months, the new ship Viking Sally (later MS Estonia) was delivered and replaced the Diana II on the Stockholm-Turku route. The Viking Sally was partly designed according to the same plans as the Diana II, but with several changes made, the final result was almost entirely different from her. Diana II moved back to Kapellskär–Naantali line until 1989, except for a short period in the summer of 1982 when she temporarily served the route Stokholm–Turku.

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

In 1989 the Finnish shipyard Wärtsilä Marine went bankrupt. Rederi AB Slite was badly affected by it, suffered from a great economic loss and was forced to sell the Diana II to PK Finans, but soon the ship was chartered back to AB Slite  and both the name of the ship and the route remained unaltered.

In 1992 the economic situation worsened for AB Slite and they had to give up operating the vessel. PK Finans sent her to Trelleborg–Rostock line on December 30.
The Diana II served on her new route until September 1994 when she was sold to Nordström & Thulin and Estonian Shipping Company who renamed her Vironia with the intention of putting her into service within the Estline service between Stockholm and Tallinn together with MS Estonia.

At a tourist fair in September the name Vironia won the competition that was organised to get a proper name for the ship. On the night of the Estonia catastrophe on board were also crew members of Diana II who were on their way to welcome the ship in Rostock.

Before entering a new line, the repairs of the vessel in Naantali were more extended than planned due to the Estonia catastrophe because the bow visor construction of the Estonia, which caused her sinking, was the same type as that of the Vironia. And before that even Diana II experienced the same kind of situation. The bow visor of the Diana II was sealed (welded shut) and a collosion bulkhead (’duck tail’) was added at the stern.

As a result of the disaster, the Vironia was renamed to avoid association with the sunken ship due to the similar name. She eventually entered service named MS Mare Balticum on the route Stockholm-Tallinn on November 11, 1994. Two years later, Nordström & Thulin acquired another former Viking Line’s vessel, MS Anna Karenina. She was renamed Regina Baltica and replaced the Mare Balticum in August 1996.

Later, Tallink began to lease the ship and she served on the route Tallinn-Helsinki renamed MS Meloodia. The first trip took place on September 20, 1996, and the last one on December 31, 2006. In 2002 Tallink bought the Meloodia and sold her in November 2007 to a Singaporean enterprise Equinox Offshore Accommodation, which is controlled by Norway. Pursuant to the contract, the vessel reached Singapore in December 2007. After reconstruction she became an accommodation and repair vessel and, thus, is known as ARV 1.