NMS Marsuinul (The Porpoise) was a submarine of the Romanian Navy, one of the few warships built in Romania during the Second World War.

She spent almost a year undergoing sea drills and tests, along with Rechinul, only being declared ready for action in April 1944.

She carried out only one patrol mission, between 11 and 27 May 1944, along the Turkish coast, between Eregli and Trabzon, and near the Soviet port of Batumi.

Shortly after she departed, she was attacked by German warships off Varna, Bulgaria, after being mistaken for a Soviet submarine.

[6][7] The German Propaganda Department made the most of the launching of the two Romanian submarines in May 1941, implying that these would be the first of a steady supply which would reinforce the Axis in the Black Sea.