In the 1980s, Iraq and Iran attacked each other's petroleum industry in the Persian Gulf in what became known as the Tanker War. In an effort to restore stability to the world's oil markets, the United States deployed a U.S. Navy flotilla to escort convoys of oil tankers in an operation dubbed Earnest Will. Although U.S. leaders imagined the Navy's presence would deter hostile action, the United States instead found itself embroiled in a secret war with Iran.During Operation Earnest Will, U.S. Navy minesweepers and Explosive Ordnance Disposal technicians kept commerce lanes clear of Iranian mines. U.S. Navy Special Boat Units and U.S. Army Special Operations helicopters interdicted the Iranian fleet of gunboats and minelayers. At a time when U.S. Navy planning focused on carrier battle group operations against the Soviet Navy, surface combatants and minesweepers found themselves taking the leading role against a regional power. As the conflict escalated, the U.S. Navy decimated the Iranian fleet in a one-day war called Operation Praying Mantis.Though the United States would triumph over Iran, great tragedy came first. On July 3, 1988, USS Vincennes mistakenly shot down an Iranian commercial flight, and all 290 passengers perished. Though gravely tragic, this event provided Iran's religious leader a face-saving means to end the Iran-Iraq War. Even as Ayatollah Khomeini accepted a peace treaty, he stated, "Taking this decision is more deadly than drinking from a poisoned chalice."Although the Iran-Iraq War ended, Operation Earnest Will led to all the American conflicts in the modern era-the wars in Iraq, the Global War on Terrorism, and the attacks brewing today between the U.S. Navy and Iran's Houthi proxies in Yemen. In A Poisoned Chalice, former U.S. Navy Commander Stephen P. Phillips discusses the Iran-Iraq War's strategic implications, what happened at operational and tactical levels of warfare, and what the war teaches us about the United States' relationship with the Middle East today.