Just prior to the Six Day War in 1967, the United States updated an emergency plan aimed at preventing Israel from expanding its territory. In May 1967, one of the U.S. commands was charged with the task of removing the plan from the safe, refreshing it and preparing for an order to go into action. This unknown aspect of the war was revealed in what was originally a top-secret study conducted by the Institute for Defense Analyses in Washington. An institute expert, L. Weinstein, wrote in February 1968 a classified document called “Critical Incident No. 14,” about the U.S. involvement in the Middle East crisis of May-June 1967. Only 30 copies of his study were printed for distribution at that time and just recently the material has been declassified.
According to Weinstein, the Joint Chiefs of Staff sent a cable on May 20, 1967, asking that Strike Command, the entity that was to have launched the attack on Israel (and was subsequently replaced by what is now Central Command), refresh the emergency plans for intervention in an Israeli-Arab war: one plan on behalf of Israel and the other on behalf of the Arabs. The basis for the directive was Washington’s commitment to the Israeli-Arab armistice lines of 1949. The United States would not allow Egypt or any combination of Arab states to destroy Israel; it also would not allow Israel to expand westward, into Sinai, or eastward, into the West Bank.
The United States had applied this policy in pressuring the IDF to withdraw from El Arish in Operation Horev in 1949 and from Sinai in 1956. A version of it would appear in Henry Kissinger's directives after the IDF encircled Egypt's Third Army at the end of the Yom Kippur War of 1973.
General Earle Wheeler, chairman of the Joint Chiefs of Staff, barred the distribution of the plan to subordinate levels. A preliminary paper was prepared by June 5, the day the war erupted, and became outdated even before it could be used.
Two retired IDF major generals, Israel Tal and Shlomo Gazit, who was then head of research in Military Intelligence said, many years after, upon hearing the secret plan of the U.S. military, that Israel had no knowledge of this.
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Sources: Haaretz (April 23, 2007)