On 7 May 1940 the German occupiers of Trondheim confiscated Nordnorge and replaced her Norwegian crew with Kriegsmarine personnel from the destroyers Paul Jakobi and Theodor Riedel. Late in the evening of 9 May the ship sailed northwards from Nyhavna under Norwegian flag, carrying a 300-strong force consisting of a company of mostly Austrian Gebirgsjäger troops from the 138 Mountain Regiment of the 2nd Mountain Division, reinforced with a heavy mortar platoon and two mountain guns. The troops and their equipment had been loaded at Muruvik near Hell. In Operation Wildente, the Germans aimed at using the Norwegian coastal steamer to bring their own troops the 500 kilometres (310 mi) to Hemnesberget, well behind the Allied lines which were south of Mo i Rana. A successful operation would break up the Allied defence line in Nordland county and cut off Norwegian and British forces, leaving the way north open for the advancing Germans, which at that point were struggling to move forward in the Mosjøen area. The operation had originally been initiated on 8 May, but had been recalled after reports of Allied submarine activity in the area. While Hauptmann Anton Holzinger led the operation, Kapitanleutnant Ernst Vogelsang captained Nordnorge during the voyage north.^{[2][10][11][12][13][14][15]} The Germans had armed Nordnorge with two 20 mm automatic cannon and two machine guns, mounted respectively at the bridge and at the bow of the ship.^[11][16]

At 09:50 on 10 May, the Norwegian military in Mosjøen was alerted that Nordnorge was sailing north, escorted by two German aircraft. The report, from observers in Rørvik, was forwarded to the British military, who after some initial hesitation, at 11:55 ordered the cruiser HMS Calcutta and the destroyer HMS Zulu to intercept and sink Nordnorge. Delayed by German air raids on the Royal Navy base in Skjelfjord in Lofoten, the British warships only got under way at 15:00, too late to intercept Nordnorge.^[11] Nordnorge was spotted again at 12:00, by a Norwegian observation post as she passed Lyngvær. The post transmitted their sighting to the military communications central in Bodø.^[17] As it was uncertain where Nordnorge was headed, Norwegian militia and army units were alerted along the coast of Hålogaland.^[18]

Nordnorge arrived at Hemnesberget at 18:30 on 10 May 1940, after a 40-hour journey. Flying the German war flag only at the last minute, the German troops on board stormed the town.^[2] As Nordnorge approached the main quay in Hemnesberget, No. 3 Platoon of No. 1 Independent Company and some 120 Norwegian landvern troops (of Infantry Regiment 14) opened small arms fire at the ship from covered positions. After getting a hawser ashore, German soldiers attacked across the quay, engaging in close house-to-house fighting. During the fighting three German bombers attacked the town. After an hour of fighting the British and Norwegian troops pulled away from the area. Following the capture of Hemnesberget, Nordnorge was unloaded of ammunition and supplies, and Allied and German dead and wounded brought on board.^{[11][14][16][19][20]} As part of Operation Wildente, German troops were also landed by Dornier seaplanes at nearby Sund.^[19][21] The fighting in Hemnesberget cost the lives of five German and eight British soldiers, as well as two Norwegian civilians.^[20][22] In his contribution to the major work on Norway and the Second World War Norges Krig 1940–1945 in 1947, Norwegian Major General Ragnvald Roscher Nielsen called Operation Wildente “as audacious as the original invasion”.^[23]

At 20:15, Calcutta and Zulu finally reached Hemnesberget. Nordnorge was immediately sunk by gunfire and two torpedoes. The ship exploded and sank stern first in deep water.^[11] As she went down, Nordnorge capsized and tore down the quay to which she was moored. The ammunition that had been unloaded on the quay was hit by gunfire and exploded.^[24] Sixteen houses were destroyed in the British shelling of Hemnesberget, and one Norwegian civilian was killed.^[25] Several of the wounded on board Nordnorge perished when she sank.^[26] As Calcutta and Zulu left the scene, they sank the small Norwegian steamer Ranheim.^[27] Before Nordnorge was sunk, the Germans had managed to unload the two mountain guns, while the other supplies lost in the sinking were replaced the next day by seaplanes.^[28]

The German capture of Hemnesberget was followed by an unsuccessful Norwegian counter-attack from nearby Finneid on 11 May. During the initial advance of the counter-attack the Norwegian forces captured three of the German naval personnel who had manned Nordnorge, before being pushed back. On 13 May the British and Norwegian forces in the area retreated northwards. The Germans continued their advance on 14 May, while two Royal Navy ships bombarded Hemnesberget the same day, destroying around 160 houses.^[29][30][31]