"Sęp" sailed into the naval port of Hel a few days before the war started, commanded by kmdr ppor. Władysław Salamon. On 1 September, the first day the war, the submarine took up her patrol sector in accordance with the Worek Plan. On 2 September she attacked a German destroyer with a single torpedo which missed, with the destroyer responding with heavy depth-charging which damaged the submarine, causing water leaks. On 3 September "Sęp" was attacked again and suffered more damage, which caused more leaks into the ship. With her position clearly revealed to the enemy, the submarine left her assigned sector and began to sail in the direction of Gotland Island. Over the next few days she operated without contact with the enemy in the vicinity of Sweden, her crew trying to repair the damage, and her captain requesting permission to return to base in order to carry out more repairs, which was denied.