Western Union Defence Organization The Western Union Defence Organization ( WUDO ) was the defence arm of the Western Union , the precursor to the Western European Union ( WEU ) . The WUDO was also a precursor to the North Atlantic Treaty Organization ( NATO ) , and its headquarters , personnel , and plans provided the nucleus for NATO ' s military command structure . Following the standing up of NATO ' s Supreme Headquarters Allied Powers Europe , the WUDO was disestablished after three years of existence . Formation . The Treaty of Brussels was signed on 17 March 1948 between Belgium , France , Luxembourg , the Netherlands and the United Kingdom , and was an expansion to the preceding year ' s defence pledge , the Dunkirk Treaty signed between Britain and France . The Treaty of Brussels contained a mutual defence clause as set forth in Article IV : Article V set forth the obligations of Brussels Pact members to cooperate with the United Nations Security Council to maintain international peace and security , and Article VI set forth the obligations of Brussels Pact members to not enter any third - party treaties that conflicted with the Treaty of Brussels . Beginning in April , the parties to the Brussels Pact decided to create a military agency under the name of the Western Union Defence Organization . The WUDO was formally established on September 27 – 28 , 1948 . Command structure . WUDO consisted of a Western Union ( WU ) Defence Committee at the Prime Ministerial level , and a WU Combined Chiefs of Staff committee , comprising the national military chiefs of staff , which would direct the operational organization . Field Marshal the Viscount Montgomery of Alamein , British Army , was the WUDO ' s senior officer as Chairman of the Commanders - in - Chief Committee which was created on 5 October 1948 . Other nominated members of the Commanders - in - Chief Committee included : The overall command structure was patterned after the wartime Supreme Headquarters Allied Expeditionary Force ( SHAEF ) , which included a joint planning staff . The WU Combined Chiefs of Staff Committee included observers from the United States . This American liaison mission was initially led by Major General Lyman L . Lemnitzer , U . S . Army , and subsequently by Major General A . Franklin Kibler , USA . Operations . Exercise Verity was a WUDO naval training exercise involving 60 warships from the British , French , and Dutch navies held in the Bay of Biscay during July 1949 . The exercise was under the overall command of Admiral of the Fleet Sir Rhoderick McGrigor , RN , the Commander - in - Chief , Home Fleet . The 60 - ship flotilla included the British battleship ; the British carriers , and ; and the French carrier " Arromanches " . Admiral McGrigor summarized the accomplishments of Exercise Verity by noting : Following Exercise Verity , WUDO announced that a major ground military exercise was scheduled for Fall 1949 under overall command of Général d ' Armée Jean de Lattre de Tassigny . Disestablishment . When the division of Europe into two opposing camps became unavoidable , the threat of the USSR became much more important than concerns over German rearmament . Western European governments sought a new mutual defence pact involving the United States . The United States recognized the growing threat of the USSR and was responsive to this concept . Secret meetings began by the end of March 1949 between American , Canadian and British officials to negotiate such a trans - Atlantic mutual defence pact . Eventually , it would lead to the formation of the North Atlantic Treaty Organisation ( NATO ) with the North Atlantic Treaty signed in Washington , DC , in 1949 . NATO began setting up its own military command structure in 1951 , at which time the headquarters , personnel , and plans of the WUDO were transferred to Supreme Headquarters Allied Power Europe ( SHAPE ) , and SHAPE took over responsibility for the defence of Western Europe .