From Hue 1968: A Turning Point of the American War in Vietnam, by Mark Bowden (Atlantic Monthly Press, 2017), Kindle Loc. 4314-4330:
[Viet Cong Lt. Hoang] called his strategy for resisting the coming counterattack bam vao that-lung dich (“hold on to the enemy’s belt”). It was how he hoped to overcome the Americans’ overwhelming firepower. The marines would typically hammer an enemy line with bombs and shells before advancing. By “clinging to their belt,” Hoang meant keeping his men so close to marine lines that it would be too risky for them to shell—he did not believe reports that Americans would not use heavy weapons in the city. His battalion was arrayed in two flexible and irregular defensive lines, one directly across the street from the marines and another two blocks back. During an attack the front line could bend in one place and hold in another. It would hold off an assault for as long as possible, and then fall back to the second line. If the attacking marines failed to occupy and hold the block they had just taken, as had mostly been the case so far, Hoang’s men would move back up at night, always staying directly across the street. If things worked out as he planned, this would force the marines to advance with small arms alone, evening the fight. In that kind of fight, Hoang believed his men had the advantage. Most were veterans with far more experience than the marines, and so long as their lines of supply stayed open they could resist for days, maybe even weeks, bleeding the marines for every square foot.
By necessity, military commanders are realists, and to Hoang it was already apparent that the “general uprising” part of the Tet plan was not happening. While some had rallied to the cause, and others seemed willing to follow orders to help dig and carry and cook (keeping their true feelings to themselves), there had been no swell of popular support. The citizens of Hue had either fled or dug in. What he saw were people in shock over the violent disruption of their lives. Refugees ran to the countryside, if they could get there, or huddled in places they hoped would be safe: in churches, behind his defensive lines, or behind the American ones at the compound and now the university. They were not rallying to one side or the other; they were trying to stay alive. They hung close to the front lines for the same reason that he stayed close to the marines, to escape bombardment. So Hoang had no illusions about keeping Hue permanently. But he was going to make the Americans pay to take it back.