What to know about the Strait of Hormuz, which Iran says it temporarily closed for a military drill

Iran has temporarily closed parts of the Strait of Hormuz. This vital waterway sees 20% of the world's oil pass through. The move follows live fire exercises in the region. Tensions are high between Iran and the United States. The closure signals potential global economic impact. Mariners were warned of the drill. The U.S. military has not yet commented.