 Together with geologist Adolf Hoel and jurist Gustav Smedal, Hallvard became one of the main leaders of the "Greenland case" "(Grønlandssaken)" that tried to bring large swathes of East Greenland under Norwegian sovereignty.With Hallvard's inspiration, based on his experiences in Svalbard and Jan Mayen, the movement began to build a network of Norwegian trapping stations, combined with surveys and explorations of the almost uninhabited area.By 1929 the "Norges Svalbard og Ishavsundersøkelser" (NSIU) —"Norwegian Svalbard and Arctic Ocean Survey", established by Hoel in 1928, sent well-organized research expeditions to East Greenland.