Exercise Mainbrace Exercise Mainbrace was the first large - scale naval exercise undertaken by the newly established Allied Command Atlantic ( ACLANT ) , one of the two principal military commands of the North Atlantic Treaty Organization ( NATO ) . It was part of a series of NATO exercises jointly commanded by Supreme Allied Commander Atlantic Admiral Lynde D . McCormick , USN , and Supreme Allied Commander Europe General Matthew B . Ridgeway , U . S . Army , during the Fall of 1952 . Background . Naval activities in north Atlantic , 1946 - 1951 . 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 Norway during World War II confirmed the importance of the region , as Germany was able to establish bases to be established 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 multi - lateral naval exercises , including : Soviet containment strategy . Initially with his " long telegram " and subsequently in his article " " that appeared in the July 1947 issue of " Foreign Affairs " , American diplomat George F . Kennan argued that Joseph Stalin would not ( and moreover could not ) moderate the determination of the Soviet Union to undermine and overthrow Western governments following World War II , noting : " . . . the main element of any United States policy toward the Soviet Union must be a long - term , patient but firm and vigilant containment of Russian expansive tendencies . . . Soviet pressure against the free institutions of the Western world is something that can be contained by the adroit and vigilant application of counterforce at a series of constantly shifting geographical and political points , corresponding to the shifts and manoeuvers of Soviet policy , but which cannot be charmed or talked out of existence . " Kennan ' s advocacy for a policy of containment against the Soviet Union formed the basis of American foreign policy during the Cold War , giving rise to the Truman Doctrine , the Marshall Plan , and the formation of NATO . NATO command structure . With the establishment of NATO ’ s Allied Command Atlantic ( ACLANT ) on 30 January 1952 , the Supreme Allied Commander Atlantic ( SACLANT ) joined the previously created Supreme Allied Commander Europe ( SACEUR ) as one of the alliance ’ s two principal military field commanders . Also , a Channel Command was established on 21 February 1952 to control the English Channel and North Sea area and deny it to the enemy , protect the sea lanes of communication , and Support operations conducted by SACEUR and SACLANT . Operational history . 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 . Force composition . 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 . " USS " Franklin D . Roosevelt " ( CVB - 42 ) with Carrier Air Group 17 ( CVG - 17 ) : USS " Midway " ( CVB - 41 ) with Carrier Air Group 6 ( CVG - 6 ) : USS " Wasp " ( CV - 18 ) and Carrier Air Group 1 ( CVG - 1 ) : HMS " Eagle " ( R05 ) : HMS " Illustrious " ( R87 ) : Other NATO Military Exercises - Fall 1952 . Exercise Mainbrace was part of a series of NATO exercise jointly commanded by Admiral McCormick and General Ridgeway during the Fall of 1952 involving 300 , 000 military personnel engaged in maneuvers from the Arctic Circle to the Mediterranean Sea . Two exercises were conducted by NATO ' s Allied Forces Southern Europe during the Fall of 1952 . " Ancient Wall " was a series of military maneuvers involving ground small unit tactical training , land - based tactical air support , and carrier - based air support . " Longstep " was a ten - day naval exercise held in the Mediterranean Sea during November 1952 involving over 170 warships and 700 aircraft under the overall command of Admiral Carney . The objective of the Allied ( " Blue " ) forces was to dislodge enemy ( " Green " ) invasion forces from their occupying positions in the Eastern Mediterranean . Blue naval forces were centered around the U . S . Sixth Fleet , under the command of Vice Admiral John H . Cassady , USN , and its two aircraft carriers , the and . Green forces included submarines and land - based aircraft . The exercise concluded with an amphibious landing at Lebidos Bay south of İzmir , involving 3000 French , Italian , and Greek troops , including the Battalion Landing Team 3 / 2 , under the overall command of General Robert E . Hogaboom , USMC . Aftermath . The Soviet Union characterized Mainbrace , Holdfast , and other NATO military exercises as " war - like acts " by NATO , with particular reference to the participation of Norway and Denmark , while the USSR was preparing for its own military maneuvers in the Soviet Zone .