29 December 1952
(Project Blue Book, U.S. Air Force, Washington, D.C.)
Source: Fold3.com, Lindon, Utah.
Quote from the document:
“1. At approximately 1330 on 29 Dec 1952, Capt Ruppelt called Lt Col Paul H. Butman (telephone: Sterling 38000– Extension 221), Division of Military Application, Atomic Energy Commission, Washington, D.C. Purpose of the call was to coordinate the visit to Los Alamos. Col Butman has previously been briefed on the possible correlation between detection of radiation from unknown sources and unidentified flying objects by Capt Ruppelt during a visit to AEC approximately two weeks ago.”