Following the invasion of Norway and the German attack on Narvik on 9 April 1940, by 3rd Mountain Division troops led by "Generaloberst" Eduard Dietl, Løken was responsible for carrying out the Norwegian mobilization in Troms. The first task Løken carried out, in addition to the mobilization, was using the forces initially available to him to block the German forces at Narvik from advancing into Troms. Maintaining control of the central army base Setermoen was vital for the Norwegian mobilization. The forces under Løken's direct command when the Germans invaded were an infantry battalion, a mountain artillery battalion and assorted support troops. In the evening of 8 April, Colonel Løken had been ordered to send his infantry battalion and a motorized artillery battery to Narvik to defend the town, but the transfer of forces was pre-empted by the German landing. In maintaining a defensive posture with almost his entire force during the mobilization stage, Løken came into disagreement with the top leadership of the 6th Division, which wanted a swift counter-attack against the Germans as soon as possible. Despite not mounting an immediate counter-attack, Løken did move troops forward to blocking positions further south than planned, as he saw it as important to stop the German advance in the Gratangen area. Colonel Løken's more cautious approach to warfare lead to a deterioration of his relationship with the more offensive division commander, Carl Gustav Fleischer. On 19 April, Løken reported that the morale of the opposing German forces seemed to be faltering, and that most of the Germans appeared to be "below average" at skiing.