Not content to serve forever at someone else's orders, Larsen decided it was time to captain his ship. He applied to the University of Oslo in 1922, pursuing a master's degree in marine engineering. Four years later, he obtained the title of Master mariner, the highest possible certification for sea captains in Norway. For the next three decades, he captained countless merchant vessels. He started with a single ship, the Skinnende Horizont (Shining Horizon). Eventually, he was the owner and captain of dozens of ships around the Atlantic - from fishing vessels to cargo ships. During the pre-war years, Larsen's whaling fleet was legendary for its size and speed. Nils Larsen was a natural leader that inspired confidence in those who served under him; men followed him willingly into danger because they knew their captain would always have their backs.