In 1906-7, Mikkelsen and Ernest Leffingwell led the Anglo-American Polar Expedition to north Alaska and northwestern Canada. The party wintered over at Flaxman island, and made several sledging trips over the ice of the Beaufort Sea in search of new land, the primary aim of the expedition. However, the expedition ship was lost, and after some hardship the crew returned to safely aboard a whaler. In spite of this set-back, the expedition made some significant surveying and other observations.