Originally named Vârtej by the Romanians, she was renamed Nibbio and classified as a scout cruiser in Italian service.

After Romania entered World War II with the Axis invasion of the Soviet Union on 22 June 1941 (Operation Barbarossa), Mărășești was limited to escort duties in the western half of the Black Sea during the war by the Soviet Navy's powerful Black Sea Fleet, which heavily outnumbered Axis naval forces there.

The scouts carried enough fuel oil to give them a range of 1,700 nautical miles (3,100 km; 2,000 mi) at a speed of 15 knots (28 km/h; 17 mph).

[2][4] Commissioned on 15 May 1918,[2] Nibbio entered service in time to take part in the final months of World War I.

She operated mainly in the Adriatic Sea, participating in the final stages of the Adriatic campaign against Austria-Hungary and the German Empire, taking part primarily in small naval actions involving clashes between torpedo boats and support operations for Allied motor torpedo boat and air attacks on Central Powers forces.

Sources disagree on the purpose of the operation: According to one, the three scout cruisers were tasked to operate about 15 nautical miles (28 km; 17 mi) west of Menders Point while the torpedo boats attacked Austro-Hungarian merchant ships about 15 nautical miles (28 km; 17 mi) to the east at Durrës (known to the Italians as Durazzo) on the coast of the Principality of Albania,[6] while another claims that they were covering the recovery of a broken-down flying boat that had landed in the Gulf of Drin.

At 14:00 that day she arrived at the island of Korčula (known to the Italians as Curzola) in the Adriatic Sea and took possession of it on behalf of the Kingdom of Italy, an action the local Slavic community strongly opposed.

[14] Massively outnumbered by the Soviet Union's Black Sea Fleet, the Romanian ships were kept behind the minefields defending Constanța for several months after the start of the war.

Beginning on 5 October, the Romanians began laying minefields to defend the route between the Bosphorus and Constanța; the minelayers were protected by the destroyers.

On the nights of 22/23 and 24/25 June, Mărășești, Regina Maria and her sister Regele Ferdinand covered the laying of defensive minefields off Odessa.

After Sevastopol surrendered on 4 July to the Axis, a direct route between the port and Constanța was opened in October and operated year-round.

[15] Mărășești and Mărăști and two gunboats were escorting a convoy of three cargo ships on 7 July 1943 when they were attacked by a small wolfpack of three submarines.

The submarine D-4 sank the German 4,627-gross register ton (GRT) freighter Santa Fé off Yevpatoria despite an escort of Mărășești and three smaller ships on 23 November.

[14] Successful Soviet attacks in early 1944 cut the overland connection of the Crimea with the rest of Ukraine and necessitated its supply by sea.

Adolf Hitler suspended the evacuation on 27 April, but relented on 8 May after further Soviet attacks further endangered the Axis forces in Sevastopol as they closed within artillery range of the harbour.

Mărășești made one trip to evacuate Axis troops and was part of the last convoy to reach Sevastopol on the night of 11/12 May.

Mărășești and Regina Maria covered the minelayers Amiral Murgescu and Dacia as they sealed off the gap that led to Sevastpol in the minefields defending Sulina on the night of 25/26 May.