Can you link to where you encountered this?

Its possible they were discussing the issue of Haiphong Harbor which was the main port of imports and exports for all of the North and very close to Hanoi. All told it accounted for nearly 50% of the international trade from the North including crucial military supplies, coal, and other materials. It was repeatedly targeted during the war under both Rolling Thunder and even more later under Linebacker I and II up to and including the dropping of aerial mines.

But without more context its hard to say.