In May 1945, he was assigned to Air Force headquarters as chief of the Strategy and Policy Division. In December 1945, he was detailed to the United Nations Military Staff Committee where he held roles as deputy and chief U.S. Air Force delegate to the committee. In August 1947, he was promoted major general and returned to Air Force headquarters serving in planning and intelligence roles and became director of Air Force Intelligence in May 1948. In 1949, Cabell set up Project Grudge to "make a study reviewing the UFO situation for AF HQ." However, Grudge quickly became all but moribund, while simultaneously reporting that all UFO cases were being closely investigated. When Cabell learned of this, he ordered Grudge dissolved and ordered that the "open minded" Project Blue Book be created.