Devised and vigorously promoted by Sir Winston Churchill, the Prime Minister of the United Kingdom, the plan was opposed by all the senior British and Allied commanders, who considered it impractical because of insufficient air support and of limited value.

In 1940, British and French plans to prevent exports of Swedish iron ore from Norwegian ports were preempted by Operation Weserübung, the German invasion of Denmark and Norway, which commenced on 9 April 1940.

[3] The German naval and air assets based in Norway were well placed to attack the British Arctic convoys, which began taking supplies to the northern ports of the Soviet Union in September 1941.

In a meeting on 24 September, Churchill refused to accept the report prepared by the Chiefs of Staff, and they reluctantly agreed to pass the matter on to General Sir Alan Brooke, then the Commander-in-Chief, Home Forces, for further consideration.

[8] Brooke recorded in his war diary on 3 October 1941,[9] that a messenger had arrived at midnight with orders to prepare a plan to attack Trondheim in one week and that he was to go to Chequers, the prime minister's country house, that evening to discuss the idea over dinner.

[15] Not deterred by his earlier rebuttal, Churchill set out his "constructive plan" in a memorandum headed Operation Jupiter dated 1 May 1942, addressed to Major General Hastings "Pug" Ismay, the Secretary of the Chiefs of Staff Committee.

Abandoning the idea of taking Trondheim, Petsamo area on the north coast of Finland would be the site of an initial seaborne assault by a division-sized force, while a brigade would capture the airfield at Porsanger Fjord.

In a memo dated 8 June 1942, they restated their objections based mainly on insufficient air cover, this time compounded by the autumn and winter weather in which the operation was expected to be carried out.

Weight was added to the argument by Vice Admiral Louis Mountbatten, the Chief of Combined Operations and a protégé of Churchill's, who unexpectedly wrote to the director of naval planning, saying that Jupiter was "impractical" and that no further time should be spent on the project.

Churchill managed to keep the Jupiter idea alive, even suggesting that Project Habakkuk, a plan for a giant aircraft carrier made from a mixture of ice and sawdust, might solve the air cover issue.

As a final ploy, Churchill referred Jupiter to Lieutenant-General Sir Frederick Morgan, who was the Chief of Staff to the Supreme Allied Commander and was responsible for the Overlord planning.

[26] The failure of Roosevelt and the Joint Chiefs of Staff to agree to Jupiter finally sealed the fate of the plan, and Alanbrooke hoped on 25 September 1942 that he was "giving up the idea of the North Norway attack".