Operations became increasingly dangerous as the war progressed and the German forces improved their air and sea defences. They began to understand the true role of fishing-boats operating far from the coast and the fishing boats were phased out in favour of three American 'sub-chasers', which were much larger, faster and better-armed, altogether better suited to the changed circumstances. The commanders of these three vessels were required to be commissioned officers and Larsen became the captain of the HNoMS "Vigra". In all he made 52 trips to Norway.