[1] Melberg then received research funding from NAVF to study Celtic languages, staying in Ireland, Wales, Scotland, and Brittany for long periods.
During the occupation years in Norway, Melberg was one of the leaders of XU Pan, a spy organisation that collected secret German information and transmitted it to London.
[2] From 1940 to 1943, Melberg worked as a jiu jitsu instructor at his brother Sam's training institute in Oslo.
Melberg wrote the introductory chapter titled "Vitenskapen å slåss" ("The Science of Fighting") to Sam's book, 'Jiu Jitsu'.
In September 1945, Melberg presented the first version of his hypothesis on the origin of the Scandinavian nations to the Norwegian Science Academy in Oslo.