This refers to the semi-fiction book written by Gayle Rivers (a pseudonym, I suppose.) It was a small multi-national force sent to assassinate Vo Nguyen Giap and several top generals inside China. The force went on foot, beginning from the border between Thailand and Vietnam (not sure about that.) Their only support was arms and ammo caches left by green berets and a radio.
The mission was aborted just as they entered China and most readers felt it was just a military experiment to see how far and how long a crack group of soldiers could fight dismounted, with minimum support.
I read the book twice. The second book was a later edition that had a short editor’s note at the end: “Gayle Rivers was the youngest in the group but he was named second-in-command. His target was Giap.”