Those would be USMC H-34s.
I had the opportunity to work with one of these birds one day, as I had 3 guys to get out of the Bush for an in country R&R. All went well as he came into my LZ and I loaded my 3 boys aboard. The chopper then attempted to lift off, to no avail. The crew chief kicked off one of my boys and they tried to take off again, this time they got about 3-4 feet into the air before settling back on the LZ, no luck. The crew chief kicked off the 2nd of my boys, leaving Mike the only one aboard. He attempted to lift off again and the pilot was still having a hard time getting aloft, I could see the crew chief pushing Mike to the hatch to kick him off, but as they were now about 6 foot off the ground, Mike was clutching the sides of the hatch as the crew chief was trying to push him out the door. This struggle went on until they reached about 15 foot in the air at which time the pilot pointed the nose of the chopper down the slope we were on, and started picking up speed to provide more lift. Needless to say, Mike went on his R&R, and I had one hilarious memory that still resides in my minds eye. Mike Knowland about 6'6" tall standing in the choppers hatch holding on for dear life as the crew chief was trying to boot him off. As the chopper dropped down the slope, I could still see Mike standing at the hatch holding on. It was the only time during my ToD that I worked with this tired old warbird, though I did hitch a ride on one from LZ Stud to Quang Tri when I went on my R&R.