Operation Jupiter was a plan originating in 1941 for an invasion of northern Norway and Finland by Allied forces during the Second World War. The first versions of the plan were code named Operation Dynamite, Operation Ajax and Operation Marrow. 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. The scheme was eventually abandoned in favour of the Normandy landings.