One of the most significant events in the history of Allied Command Europe (ACE) was France’s withdrawal from NATO’s integrated military structure. This move forced SHAPE and several other ACE headquarters to leave French territory.
In an eerie reflection of 21st century politics, the divisiveness between France and NATO’s military structure had been brewing for a number of years, as successive French governments had become increasingly incensed with what they perceived to be Anglo-American domination of the command structure and insufficient French influence throughout the command.
In December 1965, French President Charles de Gaulle had just been elected for the second time and France had acquired its own nuclear capability. De Gaulle's efforts to establish a Franco-British–American Security Directorate and gain some French influence over US nuclear weapons based in France had failed, and he hoped to gain a more independent role for France in order to maximise its future global influence and status.
President de Gaulle also disagreed with the United States’ intention to replace the strategy of the so-called Massive Retaliation with Flexible Response because he believed that this meant a weakening of the US commitment to defend Europe with nuclear weapons.
As he became increasingly critical of the developments in NATO, de Gaulle described the military integration practised at SHAPE and its subordinate headquarters as obsolete and said that it was designed to ensure French subordination to US policy.
In February 1966 President de Gaulle stated that the changed world order had "stripped NATO of its justification" for military integration and that France was therefore justified in re-asserting her sovereignty over French territory.
Consequently, all allied forces within France’s borders would have to come under French control by April 1969. Soon afterward, France stated that it was withdrawing from the headquarters of Allied Command Europe and that SHAPE and its subordinate headquarters Allied Forces Central Europe (AFCENT) must leave French territory by April 1967.
The allies were unsuccessful in their efforts to persuade the French government to reconsider, and France then withdrew the vast majority of its military personnel from NATO military headquarters in July 1966.
The other Allies moved quickly to find new hosts for the headquarters that would have to leave France, and they decided to move NATO’s political headquarters from French territory as well.
The Netherlands was selected to host AFCENT, and Belgium became the host nation for both NATO and SHAPE. SACEUR Lemnitzer had hoped that SHAPE could be located near to NATO Headquarters, as had been the case in Paris, but the Belgian authorities decided that SHAPE should be located at least 50 kilometres from Brussels, NATO’s new location, because SHAPE was a major wartime military target.
They also said that SHAPE had to be placed on land already owned by the government in order to limit costs and construction time. The Belgian government then offered Camp Casteau, a 200-hectare Belgian Army summer training camp near Mons, which was an area in serious need of additional economic investment.
To overcome SHAPE’s objections about the distance from Brussels, the Belgian government agreed to build a high-speed motorway connecting Mons and Brussels. In September 1966 NATO agreed that Belgium should host SHAPE at Casteau.
Six and a half months remained before the French deadline for SHAPE to leave France would expire. A massive seven-day-a-week building programme began, co-ordinated between the Belgian central and local authorities, the building consortium and SHAPE. Highest priority was given to building command and control facilities.
SHAPE closed its facility at Rocquencourt near Paris on 30 March 1967, and the next day held a ceremony to mark the opening of the new headquarters at Casteau. SACEUR Lemnitzer called the construction effort "a miracle of achievement" and praised the Belgian authorities and workmen for their efforts to ensure that SHAPE had a new headquarters in a remarkably short time.
The headquarters' new home in Mons, Belgium, was the center of international attention from time to time as new Supreme Allied Commanders came and went, with one of the more notable being General Alexander M. Haig, Jr., who was promoted over numerous ranking officers to become a four-star general immediately following his role as White House Chief of Staff for President Richard M. Nixon. Mons and the surrounding region are the home to a number of important historic events, the significance of many of which were lost of the foreign service personnel who served there.