The German plan was not realized due to the perceived risk of the operation, as even though an invasion of Iceland was considered possible, defence and resupply was not given British naval supremacy.
[2] During the First World War Denmark had remained neutral, and Iceland, governed directly from Copenhagen at the time, had not played a significant role in the conflict.
[3] Karl-Jesko von Puttkamer, a naval representative on the Supreme Military Council also recalled Hitler suggesting an invasion of the island in meetings in the spring of 1940.
These ships were included as they were particularly fast, could make the transit from Tromsø in German-occupied Norway to Iceland in less than three days, and were already being prepared as troop-transports for the relief of German forces at Narvik.
Bremen was to be equipped with two ferries to carry troops ashore whilst a suitable docking location was secured, and four weeks' supplies were to be brought to sustain the invasion force.
[10] This battlegroup was already in Norway at Tromsø and earmarked for the relief of Narvik, having been issued with German and Norwegian vehicles for additional mobility, and reinforced with tank, engineer, motor, and motor-cycle reconnaissance detachments.
The plan predicted the complete conquest of the island, and the overwhelming of its British garrison (at the time a single brigade reinforced by a docking operations company), within four days of the invasion.
Admiral Raeder, commander of the German navy, whilst recognising the strategic necessity of eventually occupying Iceland in order to break the British blockade that in his view presented a "continuous and unbearable threat to German safety", considered the plan highly risky given the "impossibility of continuous supply" of the invasion force and that it would "require the full employment of the navy".
[7] Raeder, after the meeting in which Ikarus was cancelled, cast doubt on the ability of Germany to carry out the plan, stating that "the task consists of transferring large numbers of men and quantities of materiel to waters for the most part controlled by the enemy".
[3] After the end of Operation Weserubung, German naval theorist Wolfgang Wegener assessed it as an incomplete victory due to Germany's failure to conquer Iceland and the Faroes.
Schuster went on to say that "The basic strategic concept for a German seizure of Iceland was sound" and that "Despite the long odds, then, had Icarus been successfully executed by Germany, the island's loss would have had a disastrous effect on the Allied war effort."