on 27 august 1939, in anticipation of war with nazi germany, the french navy planned to reorganize the mediterranean squadron into the fhm of three squadrons. when france declared war on 3 september, the reorganization was ordered and the 3rd light squadron, which included the 5th and 9th scout divisions with all of the "vauquelin"-class ships, was assigned to the 3rd squadron which was transferred to oran, french algeria, on 3 september. on 5 april 1940, the 5th scout division with "le chevalier paul", "tartu" and "maillé brézé" was assigned to force z in anticipation of an allied invasion of norway; their mission was to escort convoys between scotland and norway. the german invasion on 9 april preempted the allies and "tartu" did not begin her escort duties until mid-april when she covered convoy fp-1 transporting the 5th demi-brigade of mountain infantry () to participate in the namsos campaign on 19 april. on 24–27 april, the ship escorted convoy fp-2 conveying the 27th demi-brigade of mountain infantry to harstad, norway, to join the battle of narvik. on 3–4 may she joined "le chevalier paul", the destroyer and the british destroyers and in an unsuccessful attempt to intercept a german convoy. the 5th scout division returned to toulon on 27 may as the mediterranean fleet was developing plans to attack the italians in case they decided to join the war. after the italians declared war on 10 june, the fleet planned to bombard installations on the italian coast. "tartu" and the rest of the 5th scout division were among the ships ordered to attack targets in vado ligure. the destroyer was tasked to bombard the nafta oil tanks. two italian mas boats on patrol attempted to attack the french ships, but only one was able to launch a torpedo before they were driven off with light damage by the french defensive fire. damage assessments afterward revealed that little damage had been inflicted despite expending over 1,600 rounds of all calibers during the bombardment.