The unit was operated initially by a large number of small fishing boats, and later augmented by three fast and well-armed submarine chasers – Vigra, Hessa and Hitra. Crossings were mostly made during the winter under the cover of darkness. This meant that the crews and passengers had to endure very heavy North Sea conditions, with no lights, and constant risk of discovery by German aircraft or patrol boats. There was also the possibility of being captured whilst carrying out the mission on the Norwegian coast. However, early on it was decided that camouflage was the best defence and the boats were disguised as working fishing boats, with the crew as fishermen. The fishing boats were armed with light machine guns concealed inside oil drums placed on deck. The operation was under constant t