The NVA had set up "golden hose" AAA (anyone know what piece that was? a Gatling-type weapon, maybe?) on literally every hilltop, with interlocking fields of fire; they were actually shooting down at the U.S. helos as they went by. We lost several dozen veteran helicopter pilots in that SNAFU. Operational security failure: GVN was rotten with VC spies, the op was totally compromised from the git.
Not that we were exempt from security compromises: I've never heard the name of whoever it was who tipped the North Vietnamese about the Son Tay raid. The ARVN's were completely cut out of that for security reasons, to no avail.
Son Tay was a fiasco because of the US cloud-seeding program--the river had flooded, requiring the prisoners to be evacuated.
As for Lam Son 719--that wasn't so much the fault of Marvin the ARVN as it was the fault of Chief Petty Officer John Walker, United States Navy.