Informal attacks like the car bomb in front of the US embassy (I think March 30 1965) were very effective in destabilizing the south and making it hard to live a normal life for the civilians. Why did the US not send S. Vietnamese troops north in plain clothes to do the same? Or did they?
To date i am unaware of any "terrorist" styled actions being carried out on the N.Vietnamese. However any revelation of the CIA carrying out informal bombings wouldnt be the first time they have conducted such activity