When President Trump announced tariffs on steel and aluminum imports this month, he said protecting the two industries was vital for national security.
"We want to build our ships. We want to build our planes. We want to build our military equipment with steel, with aluminum from our country," he said at a March 8 White House news conference.
In other words, the U.S. military should be as self-sufficient as possible, and not rely on other countries to supply the essential materials it needs for defense.