What a perfect night for a weapon of mass destruction.

It was December 2, 1943. And the Nazi bomber crews flying over the Italian port of Bari might have wondered whether they were actually in a war zone.

Gleaming below, despite the wartime blackout, was a harbor so brightly lit that it illuminated more than than thirty ships supplying the Allied armies advancing up the Italian peninsula. Aboard those transports were the usual necessities of modern warfare: ammunition, fuel, food, spare parts.

Except one ship was different: the American Liberty ship John Harvey. That blandly named vessel carried one hundred tons of mustard gas, contained in hundred-pound bombs, which the United States had sent to the Mediterranean in case Hitler unleashed chemical weapons in a last desperate bid to stave off the invasion of Fortress Europe.

Surely a ship packed with poison gas would have bristled with defenses against air attack? Yet by the end of 1943, the Allies had grown complacent: Hitler’s Luftwaffe was on the defensive, the wings of its once-vaunted bomber force clipped and its fighters withdrawn back to Germany to battle Allied strategic bombing offensive.

Yet underestimating the Germans was always a mistake. The Luftwaffe was actually far from finished. It had been conducting sporadic bomber raids since the Allies landed in Italy in September 1943, enough that any prudent planner would have ensured ample fighters and flak defended a vital supply port like Bari. Yet on that December night, Bari had neither.

The countdown to disaster began on the afternoon of December 2, when a German reconnaissance plane noticed the ships crowding the harbor. Unable to pass up such a juicy target, the Luftwaffe quickly mustered 105 Ju-88 twin-engined bombers capable of dropping up to three tons of explosives apiece.

At 7:25 p.m. that night, a few German aircraft dropped chaff (metal foil) to fool defensive radar, and flares to illuminate the target. Neither was needed.

“Although the raid only lasted 20 minutes, the results were spectacularly successful for the Germans,” wrote U.S. Navy Captain D.M. Saunders in a 1967 article in Proceedings magazine. “Not since Pearl Harbor had the Allies lost so many ships at one time. Hits on two ammunition ships resulted in explosions of major proportions which shattered windows seven miles away. An oil pipe line on a quay was severed and the gushing fuel soon ignited. Oil and gasoline from burning tankers contributed to this tremendous sheet of waterborne flame which spread over much of the harbor. Ships otherwise unscathed were now enveloped in fire. All told, 16 ships carrying 38,000 tons of cargo were totally destroyed and eight others damaged that night.”

If only that had been the worst of the horror. The John Harvey’s cargo had not yet been unloaded when German bombs destroyed the ship. The mustard-gas bombs had not been armed, so they didn’t explode. Nor did they need to, because the ruptured bomb casings allowed liquid mustard to leak into harbor waters shimmering with spilled oil and teeming sailors abandoning their burning ships. Still more mustard drifted through the air as vapors.

As chemical weapons go, mustard gas wasn’t the worst, especially compared to ultra-deadly Nazi nerve gases like sarin. But mixed with spilled oil and gasoline, it clung to survivors as well as the rescuers pulling them out of the water.

Even then, the victors could have been properly treated. Mustard gas (named for its odor, which has been compared to the smell of garlic) had been used extensively in World War I, so doctors knew that victims should be washed off and given uncontaminated clothes. The problem was that the John Harvey’s cargo was so secret that most people at Bari didn’t know there was mustard present. “Many of the survivors who had been in the water, and those who had had oil splashed on them, appeared in good condition and were sent to an Auxiliary Seamen’s Home still clothed in their contaminated garments,” Saunders writes. “Others who appeared to be suffering from shock were merely wrapped in blankets, given warm tea and left alone for 12 to 24 hours— still covered with ‘oil.’”

Within a day, medical personnel were puzzled by strange symptoms appearing among sailors, rescuers and Italian civilians. Blast injuries and shock were to be expected from a bombing raid, but not burning eyes and skin blisters. Some 628 victims were afflicted, with eighty-three dead within a month. The Allied high command eventually sent a doctor familiar with chemical warfare to Bari. Though even he wasn’t informed of the John Harvey’s deadly cargo, he deduced that mustard gas had caused the symptoms, and was able to advise medical personnel (for which he was honored by the U.S. Congress in 1988).

To be fair, Allied leaders worried that publicly disclosing that mustard gas had been sent to Italy would invite Nazi retaliation. But such a disaster could not be hidden for long. In February 1944, the Allies had to admit the incident, accompanied by an assurance that they were not contemplating first use of chemical warfare.

In the end, the mustard gas shipped to Bari proved unnecessary. The Nazis did not employ chemical weapons on the battlefield (though contrary to what President Trump’s press secretary suggested, they did use poison gas to murder millions of Jews and other victims in the death camps). There was no need for the Allies to resort to them, because they were able to defeat the Third Reich with their armies—though they did need two atomic weapons to bring about Japan’s surrender.

By the end of World War II, Europe had been devastated by bullet and bomb. Yet at least it had been spared the horror of chemical warfare. Unfortunately, since 1945, the peoples of Syria, Iraq, Kurdistan and Yemen cannot say the same. Bari is a reminder of how tragic their fate is.

Michael Peck is a contributing writer for the National Interest. He can be found on Twitter and Facebook.

Image: Chemical, biological, radiological and nuclear defense training on Joint Base Elmendorf-Richardson, Alaska. Flickr/Department of Defense