Rollem was a second lieutenant conscript in the Norwegian Army when war broke out in Norway. Rollem began driving to the front at Trøndelag on 11 April 1940, two days after the invasion began. However, a German paratrooper landing at Dombås prevented him from reaching the front, so he travelled to Hamar to join up with the 2nd Dragoon Regiment (DR 2). With DR 2 Rollem fought in several battles to prevent the German advance, including in Gudbrandsdalen, and was at Åndalsnes when the Norwegians surrendered in Southern Norway.