Iran has long asserted that it can shut down the Strait of Hormuz. While the strait can't be "closed" in the traditional sense - like shutting a road - Iran could attempt to make the waterway too dangerous for commercial passage, effectively disrupting global shipping.

Pentagon officials are trying to prepare for all of the ways Iran could retaliate, as President Trump hints at what he might do.

Iran has in the past threatened to close the Strait of Hormuz to traffic in retaliation for Western pressure, and shipping sources said on Wednesday that commercial ships were avoiding Iran's waters around the strait.