C 123 Providor1
That is the beast. I worked with a small team of them when they were flying herbicide spray runs over primary jungle in Phuoc Tuy province. I would overfly at 1500 looking for any sign of ground fire aimed at them while 4-5 aircraft line abreast flew at about 200 feet agl for about a ten mile run before reversing direction. Several times I had a 2 aircraft flight of F 100's or Phantoms overhead and available for an airstrike. Several Huey Cobra gunships were also added at times.
You could see enemy tracks through the foliage of primary jungle. After the spray killed the trees bamboo quickly colonised the area exposed to sun and effectively covered up any evidence of activity.