In a simple coincidence, U.S. President Donald Trump will spend Veterans Day 2017 in Vietnam, underscoring just how much the relationship between the two countries has changed in more than four decades. If anything, he is likely to laud the Vietnamese for their help in resolving the long-standing and controversial issue of American prisoners of war and those still listed as missing in action during the fighting in Southeast Asia. But while there is absolutely no evidence to support the idea that there are still any U.S. POWs alive in the region, declassified documents show that the United States put the full power of the intelligence community to work for years so as to be absolutely sure this was the case. In the Summer 1984, as he campaigned for a second term, U.S. President Ronald Reagan personally ordered the National Security Agency and other elements of the U.S. signals intelligence community to gather as much information as possible about the potential status of Americans MIA in South East Asia. In response, U.S. Army and Air Force personnel at the Field Station Kunia listening post in Hawaii dutifully tuned their equipment toward targets in Vietnam.

“For a period of 6 months, USM-2 was assigned the mission of searching out and exploiting Vietnamese communications that might contain information on the issue,” a heavily redacted annual history of the U.S. Army’s Intelligence and Security Command for the 1985 fiscal year explained. “Upon receipt of the message, USM·2 and its Air Force counterpart, USA-32, organized a Joint task force of 39 Army and 50 Air Force operators and 22 Army analysts.” A private individual obtained a copy of the historical review through a Freedom of Information Act Request. Government transparency website GovernmentAttic.org posted a copy online in October 2017.

Arnie Sachs/Picture-Alliance/DPA/AP US President Ronald Reagan salutes supporters at the 1988 Republican National Convention.

“USM-2” and “USA-32” are known as Signals Intelligence Activity Designators, or SIGADs, which are codes for specific elements within a particular field station, which could be a fixed base on land or a spy ship. These abbreviations are used by intelligence agencies in all the members of the so-called Five Eyes intelligence bloc, which includes the United States, the United Kingdom, Canada, Australia, and New Zealand. When one activity shuts down, agencies are free to reuse the SIGAD again. The Army’s USM-2 operated from a site in Petaluma, California until 1971. In 1980, it stood up again at Kunia, as did the Air Force’s USA-32. The USA-32 element had actually been inside South Vietnam previously, situated within the American base at Da Nang until 1973, according to a declassified and heavily redacted internal NSA news item. U.S. President Jimmy Carter had ordered the expansion of signals intelligence capabilities in response to a number of growing worldwide security concerns, including the crisis in Iran and Communist insurgencies in Latin America. After taking office in 1981, Reagan had pushed for more funding to further improve their capabilities. The Kunia facility itself dates back to World War II, when the U.S. military decided to build a massive, bomb proof underground bunker following Japan's surprise attack on Pearl Harbor. Originally known as the Kunia Tunnel, it subsequently became Field Station Kunia, and then the NSA's Kunia Regional Security Operations Center (KRSOC). The U.S. Navy took over management of the site in 1995.

USN via Cryptome A view of the entrance to the KRSOC "tunnel" in 1998.

According to the INSCOM history, in July 1985, Kunia began using a new intelligence collection and distribution system, the name of which remains classified. This allowed the site to expand its capacity and take on additional missions – one of which would have been what the Army described as the “Southeast Asia Development Mission,” regarding the POW/MIA issue. That Reagan personally initiated the intelligence operation in 1984 isn’t particularly surprising. At the time, it remained a hot button issue. This was true especially within veterans communities, who were skeptical of the U.S. government’s insistence that no one had gotten left behind as the country had extricated itself from a messy and unpopular war. In 1983, the President had first proclaimed National POW/MIA Recognition Day, which the United States now observers every year on the third Friday in September. Politicians and activists were still publishing accounts from anonymous sources describing active prison camps in Vietnam, Laos, and Cambodia full of U.S. troops.

USAF US Air Force Technical Sergeant James Cook salutes the flag from his stretcher as he is carried aboard a C-141 tranport during Operation Homecoming, the repatriation of US prisoners of war from North Vietnam in 1973.

There has never been any confirmed evidence that these reports were true, but conspiracy theories remain widespread about the fate of hundreds of still missing American military personnel. So, turning already expanding intelligence resources to look into the matter, even if briefly, undoubtedly seemed liked a good idea to Reagan, who would go on to declare the final accounting of the living and the dead at one point as “the highest national priority.” That listening posts as far away as Hawaii can pick up high frequency transmission from as far away as Vietnam is itself down just to physics. To work at all, these long-range communication systems bounce radio waves off of the ionosphere in the upper atmosphere. As a result, intelligence agencies can build huge antenna arrays on the ground to stand ready to collect those signals as they come flying back down to earth. Some of the most notable of these were the eight AN/FLR-9 systems the United States put in place across the Pacific and Europe.

US Army An undated aerial shot of the AN/FLR-9 "Elephant Cage" at Field Station Augsburg in Germany.