Brit expert says the U.S. Army never really did population-centric COIN in Vietnam

Not at all, concludes a new study by J.P. Harris, a teacher at Sandhurst, the British
military academy: "It is doubtful whether a truly population-centric approach
to counterinsurgency ever really took root in the US Army during the 1960s and
early 1970s, even in its Special Forces." 

There is a bit more in this Naval Post Graduate School essay by Maj. Michael Sullivan
(on p. 27 of the book). And here, too, if you wanna get all CIDG about it. Which, as Harris says, was neither "civilian" nor
"irregular" nor "defensive," once its mobile strike force was organized.