Americans should be alarmed by recent calls for repeal of the Jones Act, a 1920 law requiring that merchant vessels navigating between U.S. ports must be manufactured and flagged in the U.S., owned and operated by American companies, and crewed by American citizens. Passed in the wake of World War I to ensure that the United States maintained a vital sea transport capacity in the event of future conflict, the law has been vital to U.S. national security and economic strength for almost 100 years.