He returned to Bergen in January 1940, stationed at an anti-air battery to guard the Norwegian neutrality in World War II. However, on 9 April Nazi Germany invaded Norway. Welle-Strand became involved in the subsequent fighting, first at the anti-air battery, later during a retreat to the mountains of Hardanger. The Norwegian troops went to Voss and Leikanger; Welle-Strand then parted ways with them and made his way via Finland and Finnmark to Tromsø. He escaped from there to England with the naval ship "Heilhorn".