What sort of picture is painted by those words, "formless" and "frontless," to describe the action in Vietnam?
These words paint a picture of a very frustrating war that would have been very hard to fight and hard to win. They paint the picture of a war that would have been very frustrating.
In a conventional war, there are fronts and the war has a clear form. It is possible to tell how one’s side is doing. For example, in World War II, it was possible to easily follow the progress of the front as it moved towards Germany after the D-Day invasions. It was not always one solid line; there would be places where the Germans were doing better or worse. However, it was clear where the fighting was and it was clear how the fighting was going.
In the Vietnam War, neither of these things was true. The fighting was frontless and could occur almost anywhere. There was no frontline because the enemy was not trying to invade South Vietnam. The fighting was formless because it did not form a clear pattern of one side advancing into the other’s territory. This made it very difficult to have any idea as to who was winning. This made the war frustrating for those fighting it and for those who had to decide whether to continue fighting.
These words, then, paint a picture of a very frustrating and difficult war to fight.