What was the word used to describe tactic attack an American merchant ship?

The word used to describe a tactic attack on an American merchant ship during the early days of World War II was "commerce raiding."

This term referred to the practice of German U-boats (submarines) attacking and sinking unarmed merchant ships carrying supplies to Allied nations.

It's important to note that while "commerce raiding" was a common term at the time, it is not a neutral term. It implies a legitimate military strategy, whereas many people saw these attacks as acts of piracy or terrorism.