In the ensuing battle, the Soviet Shchuka-class submarine Shch-206 was attacked by Năluca, at first with 20 mm rounds and then with depth charges, eventually being sunk with all hands aboard.

[6] On 15 August, the Romanian merchant Peles was torpedoed and sunk by the Soviet submarine ShCh-211 north east of Cape Emine, in Bulgarian waters, while the Italian tanker Superga was missed during the same attack.

On 14 September, the Bulgarian merchant Chipka sunk after running on a mine laid by Soviet submarine L-4, close Varna.

On 19 September, the Bulgarian auxiliary minesweeper W-2 sunk close Cape Galata due to a mine laid by Soviet submarine L-4 or L-5.

[9] On 10 October, the Romanian auxiliary minelayer NMS Regele Carol I sunk close Cape Galata after running on a mine laid by Soviet submarine L-4 or L-5.

Between 17 and 21 October, the exact date being unclear, the Soviet submarine M-58 was lost; most likely having hit a mine in the Danube estuary area.

On 26 October, the Soviet small submarine M-35 attacked, on surface, a convoy of German barges with gunfire: SF-25 was sunk and SF-36 was heavily damaged and driven ashore off Sulina.

On 3 November, the Turkish sailing vessel Kaynakdere was sunk with gunfire by Soviet submarine Shch-214 close Cape Igneada.

[17][18][19] On 17 December, near Jibrieni, the Soviet submarine M-59 attacked an Axis convoy consisting of the Hungarian cargo ships Kassa and Kolozsvár[20] and the Bulgarian cargo ship Tzar Ferdinand,[21] escorted by the Romanian Navy with the Regele Ferdinand-class destroyers Regele Ferdinand and Regina Maria, gunboats Stihi Eugen and Sublocotenent Ghiculescu, and torpedo boats Sborul and Smeul.