Supreme Headquarters Allied Powers Europe government offered Camp Casteau, a 2 km² Belgian Army summer training camp near Mons, which was an area in serious need of additional economic investment. In September 1966, NATO agreed that Belgium should host SHAPE at Casteau. 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. The drawdown of the British Mediterranean Fleet, the military difficulties of the politically decided command structure, and the withdrawal of the French from the military command structure forced a rearrangement of the command arrangements
Exercise Longstep on a renewed urgency following the outbreak of the Korean War, prompting NATO to establish Supreme Headquarters Allied Powers Europe (SHAPE) under the command of General of the Army Dwight D. Eisenhower, U.S. Army, on 2 April 1951. Exercise Longstep was an early naval exercise for SHAPE's southern regional command, Allied Forces Southern Europe (AFSOUTH). The overall exercise commander for Grand Slam was Admiral Robert B. Carney USN, NATO's Commander-in-Chief Allied Forces Southern Europe (CINCSOUTH). AFSOUTH component commanders during Longstep were: The objective of the Allied ("Blue") forces was to dislodge enemy ("Green") invasion forces from their occupying positions in