The U-boat skipper peered through his periscope and smiled. It looked like such an easy target. And indeed, it was. Yet going after it sealed his doom while also setting in motion a series of events that both made another man a hero and triggered official denial of his valor.

And it all happened right in America’s backyard.

Hans-Günther Kuhlmann, 28, commanded the U-166, a brand-new submarine in service for barely six months, sent to fight Nazi Germany’s newest enemy, the United States. She prowled the Gulf of Mexico just a few miles off the coast. It was a fertile hunting ground. In the past two weeks, U-166 had sent three American cargo ships to the bottom. Now, on the night of July 30, 1942, Kuhlmann was going after the biggest prize yet.

The SS Robert E. Lee was a steam passenger ship that carried wartime cargo. She had left Trinidad bound for Tampa, Florida. But the threat of U-boats lurking nearby had diverted her to New Orleans.

At 10:37 p.m., Kuhlmann gave the order, “Fire!” Lookouts on the Lee spotted the torpedo speeding their way. But there was no time to take evasive action. Within 15 minutes, the Robert E. Lee was another maritime casualty. All but 25 of her 407 passengers and crew were rescued.

Then the U-166’s getaway was foiled. Because Kuhlmann didn’t know the Lee had a secret ace up its sleeve.

Sailing ahead of it was Patrol Coastal 566, a small submarine chaser. While other vessels and aircraft were busily rescuing the Lee’s survivors, PC-566 had a job to do. Lt. Cmdr. Herbert Claudius turned the small ship around and raced into the torpedo’s wake at full speed. Within minutes, he dropped depth charges.

An oil slick soon oozed to the surface. Claudius radioed that he had destroyed the German sub. And that should have been that.

Except, it wasn’t.

A Navy review board investigated. It not only ruled there was no way the PC-566 had sunk the U-boat as claimed, but it even criticized Claudius’ tactics and scolded him. Utterly humiliated, he was stripped of his command and sent back to the sub chaser version of basic training. It was like an addled child being forced to repeat a school grade he had failed.

Even worse news came two days after the Lee’s sinking. A Coast Guard plane spotted and attacked a U-boat. It was credited with destroying the U-166. (In fact, it had only damaged her.)

With that, the Navy closed the book on the incident.

Claudius served with distinction for the rest of the war and afterward. Yet the stain of the incident followed him wherever he went. The men of the PC-566 adamantly insisted they had sunk a sub that night; Claudius believed so, too, right up until he died in 1981.

Then, 15 years later, new technology changed everything.

While making an underwater survey of the Gulf floor for an oil company in 1986, oceanographers discovered what appeared to be two wrecks. The first was soon confirmed as the Robert E. Lee. It took a few more years, but in 2001, the remains of the U-166 were positively identified just over a mile away.

In December 2014, Navy Secretary Ray Mabus presented Herbert Claudius Jr. with the Legion of Merit posthumously awarded to his father.

It took 72 years, but the U.S. Navy belatedly admitted that it, not the lieutenant commander, had got it wrong.

As it turned out, Claudius and his small crew had scored the only German U-boat sunk in the Gulf of Mexico in all of World War II.

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