While Nazi Germany rained conventional bombs upon Great Britain in World War II, Adolf Hitler’s forces were also busy at work devising fiendishly clever booby traps to strike the enemy on its own soil. As the war progressed, British intelligence agency MI5 learned of a secret Nazi sabotage campaign to hide explosives in everyday items such as cans of plums, canisters of motor oil, shaving brushes and lumps of coal. The spy agency even discovered Nazi plans to develop bangers and mash that delivered a true bang.

In the spring of 1943, MI5 operative Victor Rothschild learned of an even more ingenious bomb being conjured up by the Nazis—an exploding chocolate bar. The killer candy was cloaked in a black foil wrapper with gold lettering bearing the brand name “Peter’s Chocolate.” Underneath the real chocolate exterior was steel and canvas, and when a piece of chocolate at the end of the bar was broken off and the canvas pulled, it activated a bomb that would explode after a seven-second delay. MI5 believed Nazi secret agents were plotting to smuggle the explosive chocolate into the War Cabinet and into the hands of Prime Minister Winston Churchill, who was known to have a sweet tooth.

Rothschild, a trained biologist and a member of a prominent banking family, had been recruited to lead MI5’s three-person explosives and counter-sabotage unit. However, he was not an artist and needed sketches of the Nazi devices that could be used by intelligence officers to defuse the bombs. Luckily, Donald Fish, one of Rothschild’s two colleagues, knew just the right person for the job—his son.

Laurence Fish, a young self-taught artist, was employed by MI5 to produce detailed, free-hand drawings of the menagerie of booby trap bombs. When Rothschild learned of the stealth candy bomb, he again turned to Fish. “I wonder if you could do a drawing for me of an explosive slab of chocolate,” Rothschild wrote to Fish on May 4, 1943, from a secret bunker deep under the streets of London. The MI5 counter-sabotage agent included a rough sketch of the bomb, which he wanted Fish to improve upon. “Would it be possible for you to do a drawing of this, one possibly with the paper half taken off revealing one end and another with the piece broken off showing the canvas.”

The letter, stamped “secret,” had been found by Fish’s widow, Jean Bray, as she combed through her husband’s possessions following his 2009 death at the age of 89. The artist’s original drawing, though, had been missing for decades and presumed lost along with dozens of others. The BBC reports, however, that a sheaf of more than two dozen of Fish’s drawings were rediscovered this summer by Rothschild’s family as they cleaned out a chest of drawers in the family house in Suffolk, England, a quarter-century after the intelligence officer’s death. Rothschild’s daughter, Victoria Rothschild Gray, gave the sketches to Bray.

“I didn’t know that the drawings existed,” said Fish’s widow, according to an article in the Gloucestershire Echo. “He always kept the letters, but nobody knew what had happened to the drawings. We presumed that they had been destroyed or lost.”

Some of the explosive devices depicted in Fish’s newly rediscovered drawings appear to have been ripped from the pages of one of Ian Fleming’s James Bond novels. There are bombs concealed inside matchboxes, pocket watches and even Thermos flasks. One sketch even shows the Nazis had developed plans for a simple culinary timing mechanism in which dried peas in a test tube would expand as they absorbed water, forcing a floating cork to rise until two brass screws touched to complete a circuit.

Made in an era before computer-aided design, the finely drawn sketches were not only utilitarian in assisting MI5 personnel to locate and defuse booby trap devices, but artistic as well. Rothschild even mounted some of the drawings on the walls of his study. “Nowadays people would say these drawings are nothing and you could do it with a computer in seconds,” Bray said. “But there was no machinery or anything like that at the time. They were all hand drawn.”

Following the war, Fish found success working as a poster artist, graphic designer and commercial artist for major corporations, tourist boards and charity organizations. Bray hopes that a museum or archive will want the drawings for their collections.