However Lewis came to the attention of MI6, it needed Lewis in the wake of the German invasion of Norway and Denmark on April 9, 1940. Though the British sent troops to Norway to counter the German invasion, it was too late to intervene in Denmark, whose subjugation was accomplished in only one day. One month later on May 10, 1940, German forces invaded the Netherlands, Belgium, and France, and by June 22 the French government had capitulated, leaving Britain to fight on alone.
On that same morning in May, however, the British did the next best thing they could do to help Denmark and the rest of Europe: They launched a surprise invasion of Iceland, which was part of the Kingdom of Denmark. Iceland’s strategic significance in the North Atlantic had been known since the Viking voyages a thousand years earlier. Iceland sits along the arc of islands that include Britain, Ireland, Iceland, Greenland, and Newfoundland. Each island became a staging ground for pushing farther westward. In the Battle of the Atlantic, Iceland could have provided Germany with a strategic naval and air base. Instead, thanks to the British invasion, Iceland provided the ideal base for seaplanes to search for the German naval vessels that prowled the Atlantic sinking the merchant fleet with its crucial supplies.
Though British control of Iceland was critical, Britain could not afford to deploy its troops to hold the island when greater battles loomed elsewhere, beginning with the struggle for North Africa. Holding Iceland depended upon the goodwill of the people of Iceland who never had asked to be invaded by the British. If Britain retained Icelandic goodwill, then Churchill could occupy the island with reserve troops rather than his best fighting forces.