After his country surrendered to the United States in 1945, former Japanese Prime Minister Hideki Tojo had a pretty rough go of things. A failed suicide attempt left his stomach mangled (he tried to shoot himself in the heart but missed), and he had to recover in a Tokyo jail while he awaited trial for war crimes. While imprisoned, he became the butt of a prank that left a secret message drilled into his top set of false teeth, right at the tip of his tongue: "Remember Pearl Harbor."

The message was put there by a 22-year-old dental prosthetics officer with the U.S. Navy named Jack Mallory. Mallory was assigned to the 361st Station Hospital in Tokyo, which was responsible for nearby Sugamo Prison where Tojo was being held. Just one month after arriving in Japan in 1946, Mallory was handed a stupefying assignment: The architect of Japan’s war against the U.S. needed dentures, and Mallory was to make them for him.

Jack Mallory and his roommate, a dentist by the name of George Foster, were called to Sugamo Prison to examine Tojo, whose teeth were decaying and crumbling from his gums. “I knew I was going to meet an evil man," Mallory told Sierra Countis of the Chico News & Review in 2002. “It was a shock to see him. He was very humble and just a meek, little guy.”

Tojo had requested the dentures so he could speak for himself at his upcoming trial. He knew his execution was a foregone conclusion, so when Mallory suggested he get a full set of false teeth, Tojo declined and asked only for the top row—he wouldn’t be needing them for long and didn’t want to waste anybody's time.

Word of the assignment got out, and Mallory’s colleagues at the hospital egged him on to use the opportunity to pull off a legendary prank. He wanted to inscribe "Remember Pearl Harbor" on the dentures but knew such a conspicuous message would be caught easily. He decided to use Morse code instead, so he drilled the sentence into the row of false teeth as a series of dots and dashes.

Mallory and Foster always referred to it as a “prank” and not much more. “I figured it was my duty to carry out the assignment,” Foster recalled in 1988. “But that didn’t mean I couldn’t have fun with it.”

“It wasn’t anything done in anger,” Mallory told the AP in 1995. “It’s just that not many people had the chance to get those words into his mouth.”

The prank was meant to be kept secret, though news got out after someone at the dental service blabbed about it in a letter home, where the story traveled so fast that it even found its way onto a Texas radio broadcast.

With news of the deed now bouncing back to and around Tokyo, Mallory confessed to his supervisor before things could get more out of hand. “That’s funny as hell," Mallory recalled being told, "but we could get our asses kicked for doing it.” His supervisor ordered the men to undo their prank immediately.

Late one evening in February 1947—some three months after first inscribing "Remember Pearl Harbor" in Morse code into the false teeth—Mallory and Foster paid a visit to Tojo’s cell and asked the guard to wake him up. They needed to perform emergency work on his dentures, they said, and Mallory swiftly and discretely ground the hidden message off Tojo’s teeth. All reports indicate Tojo never knew it was ever there.

The next morning, a supremely pissed-off and high-ranking colonel called on Mallory and Foster to ask about the prank. With the evidence inside Tojo's mouth ground and sluiced away, the young dentists were able to soundly deny everything.

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Jack Mallory returned to the United States in 1947 and set up a dental practice in California that he ran for decades. Before he left Tokyo, however, he spent a day sitting in on Hideki Tojo’s trial. As Mallory recalled to the Chico News & Review, his former patient recognized him inside the courtroom, smiled, "pointed to his teeth and bowed toward him in thanks."

Tojo was able to speak for himself at his trial and took responsibility for Japan's actions during the war. He was found guilty and was hanged on December 23, 1948.

Jack Mallory passed away in 2013 at the age of 88. His online obituary includes stories of skiing and other outdoor adventures, plus a quick, vague aside about a "dental prank" performed on Hideki Tojo, "the 'mastermind' behind the attack of Pearl Harbor."