The strategic importance of control of Norway and the adjacent Norwegian and Barents seas was recognized by Anglo-American naval planners as early as the First World War. The invasion and Occupation of Norway by Nazi Germany during World War II confirmed the importance of the region, as Germany was able to establish bases for submarine and air operations against Allied convoys bound for the Soviet seaport of Murmansk.
Following the Second World War, several former allied navies executed a number of individual and multinational exercises, including:
Initial planning for Exercise Mainbrace was initiated by General Dwight D. Eisenhower prior to his resignation as NATO's Supreme Allied Commander Europe (SACEUR) to run for the President of the United States. The exercise itself was commanded jointly by SACLANT Admiral Lynde D. McCormick, USN, and SACEUR General Matthew B. Ridgeway, U.S. Army, with the immediate theater commander being Admiral Sir Patrick Brind, RN, who was in Commander-in-Chief Allied Forces Northern Europe.
Mainbrace was conducted over twelve days between September 14–25, 1952, and involved nine navies: United States Navy, the British Royal Navy, French Navy, Royal Canadian Navy, Royal Danish Navy, Royal Norwegian Navy, Portuguese Navy, Royal Netherlands Navy, and Belgian Naval Force operating in the Norwegian Sea, the Barents Sea, the North Sea near the Jutland Peninsula, and the Baltic Sea. Its objective was to convince Denmark and Norway that those nations could be defended against attack from the Soviet Union. The exercise featured simulated carrier air strikes against "enemy" formation attacking NATO's northern flank near Bodø, Norway, naval air attacks against aggressors near the Kiel Canal, anti-submarine and anti-ship operations, and U.S. marines landing in Denmark.
Eighty thousand men, over 200 ships, and 1,000 aircraft participated in the Mainbrace. The New York Times' military reporter Hanson W. Baldwin described this NATO naval force as being the "largest and most powerful fleet that has cruised in the North Sea since World War I."