Operation Ikarus (Unternehmen Ikarus or Fall Ikarus in German) was a World War II German plan to invade Iceland, which had been occupied by British forces during Operation Fork in 1940. The German plan was never realized.
The purpose of the British move was to prevent the German invasion of the island. In fact, German dictator Adolf Hitler was not planning to invade at the time. So, instead of discouraging the Germans, the British occupation only encouraged them.
The German plan was not realized due to the delay of Operation Sea Lion (Unternehmen Seelöwe) and, even though an invasion of Iceland was considered possible, defense and resupply was not.