He is best known for his role in discovering that during the mid-1960s American military intelligence had underestimated the number of Viet Cong and North Vietnamese Army soldiers.
He wrote on its economy, but it was political turbulence in the newly independent state that drew world attention, including Cuban under Che.
Although at first greeted with 'snickers' from intelligence agents at State, he successfully predicted the crisis appointment of Moise Tshombe by Joseph Kasavubu, then President of Congo.
His branch chief, Edward Hauck, when asked told Adams that the Vietnamese communists would probably outlast the Americans and, after 10 or 20 years, win the war.
Following his procedure per the Congo, he began assembling biographies of Viet Cong operatives, but stopped when told the names were all fake.
He drew welcome information, however, out of statistics compiled in Saigon from the files of Chieu Hoi (South Vietnam's defector program).
Yet feedback within his CIA office was ambiguous, noncommittal, cautious; they knew well enough the widespread evidence of the Viet Cong's growing success in the field, of its confidence and morale.
His report "Viet Cong Morale: Possible Indicator of Downward Drift" was published, but with caveats in footnotes and distributed only within the CIA.
Such a combined loss rate per year (10,000 defectors + 70,000 deserters), in addition to VC annual casualties (reported at 150,000), would severely reduce the Viet Cong's overall strength (which MACV's O/B put at 280,000).
"Bulletin 689" contained a single three-page document, "Recapitulated Report on the People's Warfare Movement from Bình Định Province".
From his research into captured enemy documents and other sources, he "concluded that previous estimates had undercounted the communists by hundreds of thousands.
"[29] If the Viet Cong enemy combatant count was higher, it implied that the prospects for a South Vietnamese military victory were dimmed.
MACV forcefully insisted on its lower numbers, and the CIA in 1967, due to the domestic political environment, reluctantly agreed.
Yet he persisted in advancing the higher count of Viet Cong in the 'Order of Battle' controversy, despite the institutional fallout between CIA and MACV.
"[35][36][37][38] In 1969 Adams, fearing that his opponents would destroy them, secretly removed CIA files and documents which would support his case.
In particular, the tailoring of 'pure' intelligence in order to fit the political agenda of its primary consumers: the American government, and its chief executive.
His testimony was offered to show that supposed 'secret information' in the text of the Pentagon Papers contained in reality many fictions.
Eventually, citing the "totality" of government misconduct, Federal judge William Matthew Byrne Jr. dismissed all charges against Ellsberg and Russo.
Fearful that his opponents would destroy evidence, he had already removed files and documents from the CIA, hiding them on a farm in rural Virginia.
[47][48] In 1982 Adams provided critical evidence to CBS News reporters who made the documentary The Uncounted Enemy: A Vietnam Deception.
[49][50] General Westmoreland in 1982 sued for libel against CBS News, and named as co-defendants the producer George Crile, correspondent Mike Wallace, and consultant Sam Adams.
The MACV O/B ('Order of Battle') estimate was "undercut" by "latter admissions" at trial that [The officers] had known at the time that General Westmoreland's insistence on an O/B total of no more than 300,000 was an artificial position dictated by political considerations, and that the true number of enemy forces had almost certainly been much higher.
Evidently it was testimony "by his former chief of military intelligence" in Vietnam, which agreed more with Adams, that convinced Westmoreland to settle.
He discussed the Vietnam War in 1967–68, and opined that the true calamity of the Tet Offensive was its surprise, because the public did not know the VC's real strength.