>>21726271 PB
Memorandum From the Deputy Under Secretary of State for Political Affairs (Kohler) to Secretary of State Rusk1
Weather Modification in North Vietnam and Laos (Project Popeye)
Washington, January 13, 1967.
Proposal
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The Department of Defense has requested our approval to initiate the operational phase of Project Popeye in selected areas (map at clip)2 along the infiltration routes in North Vietnam and southern Laos. The objective of the program is to produce sufficient rainfall along these lines of communication to interdict or at least interfere with truck traffic between North and South Vietnam. Recently improved cloud seeding techniques would be applied on a sustained basis, in a non-publicized effort to induce continued rainfall through the months of the normal dry season.
Background
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A test phase of Project Popeye was approved by State and Defense and conducted during October 1966 in a strip of the Lao Panhandle generally east of the Bolovens Plateau in the valley of the Se Kong River. The test was conducted without consultation with Lao authorities (but with Ambassador Sullivan’s knowledge and concurrence) and, to the best of our knowledge, remains unknown to other than a severely limited number of U.S. officials.
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During the test phase, more than 50 cloud seeding experiments were conducted. The results are viewed by DOD as outstandingly successful.
(a) 82% of the clouds seeded produced rain within a brief period after seeding—a percentage appreciably higher than normal expectation in the absence of seeding.
(b) The amount of rainfall induced by seeding is believed to have been sufficient to have contributed substantially to rendering vehicular routes in this area inoperable. Since the end of the rainy season, the communists have failed to undertake route repairs and there has been no vehicular traffic.
(c) In one instance, the rainfall continued as the cloud moved eastward across the Vietnam border and inundated a U.S. Special Forces camp with nine inches of rain in four hours.
(d) DOD scientists consider that the experiment demonstrated a capacity to raise and maintain rainfall under controlled conditions to the level at which the land is saturated over a sustained period, slowing movement on foot and rendering the operation of vehicles impracticable.
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In our view, the experiments were undeniably successful, indicating that, at least under weather and terrain conditions such as those involved, the U.S. Government has realized a capability of significant weather modification. If anything, the tests were “too successful”—neither the volume of induced rainfall nor the extent of area affected can be precisely predicted. The only absolute control, therefore, is after the fact, i.e., to halt cloud-seeding missions.
https://history.state.gov/historicaldocuments/frus1964-68v28/d274