As during the first 1941 campaign , the Soviet Navy sent submarines against the Axis supply lines along the western coast of the Black Sea . A number of neutral Turkish vessels were also attacked near the Bosporus area , resulting in the Struma disaster . Once again , Axis defenses primarily consisted of Romanian-laid fields of mines : 5000 mines were laid ( both anti-submarine and floating ) , the Soviet Navy possessed 34 submarines including 14 of new construction but only 20 were operational ready . German U-boats began operating in the Black Sea during late 1942 , without scoring any hits while the Romanian submarine Delfinul departed for her final patrols
Struma disaster
Struma disaster
Submarine warfare in the Black Sea campaigns (1942)