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World War II Code Used By British POW In Letters Home Cracked, Offering Rare Glimpse At MI9 History

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In an achievement that may have longstanding implications for World War II historians, a group of researchers at a British university has cracked the code used by a British soldier imprisoned in Germany.

Mathematicians, historians and geographers from Plymouth University in England worked together to decipher the 70-year-old coded letters sent home by Sub-Lieutenant John Pryor.

The project was spearheaded by Barbara Bond, a pro-chancellor at the university, who is working toward a Ph.D. on MI9 (a section of British military intelligence) subterfuge and escape plans during World War II. She learned of the letters through university Governor Stephen Pryor, John Pryor's son, according to a Plymouth press release.

“I had known for 30 years that my father had these letters, but he could not remember the full code and so their contents lay hidden," Stephen Pryor said in the statement. "My father was among the tens of thousands of young men who as PoWs lost the best years of their youth and could never hope to regain them. But I can now see that despite their plight, he and his peers took incredible risks and it has only made me admire their resilience and ingenuity even more.”

Bond, together with Pryor, history professor Harry Bennett and mathematics professor David McMullan, eventually was able to crack the coded letters, translating mundane anecdotes about things like vegetable patches into information on the enemy.

In an interview with The Huffington Post, Bennett said the project was "an incredible achievement" that reveals surprising details about the operational role of prisoners of war behind enemy lines.

"Suddenly, [we see that] POWs are not only trying to get out of war camps, they are also sending back information of a sensitive nature, almost becoming a kind of eyes and ears on the ground," Bennett told HuffPost.

In his letters, Pryor gave information that could help the Royal Navy prevent submarine attacks. He also identified a German weapons dump for British bombers, Bennett said.

The fact that POWs could have played a major role in the war effort is "actually quite fascinating when you think about it," Bennett added. "I don't think historians have really woken up to significance of this."

The coding was complicated, according to Bennett, who described the process as "crosswords or puzzles –- a form of super-Sudoko for the 1940s generation" in an interview with the Daily Mirror.

Decoders in MI9 would have known to look for certain letters in certain words, which would then be arranged on a grid. For example, the Daily Mail details the hidden meaning behind this seemingly innocent paragraph:

"Many seeds are left, being saved from several plants which did very well some time ago," Pryor wrote. "Our last year's harvest was extremely good. Well worth repeating again for this year."

After being decoded, the outlet notes, it becomes clear Pryor had coded this message about a submarine attack: "HMS Undine attack failure. Trawler depth-charged, scuttled in 70 feet, three burnt."

According to Bennett, some signs that an old World War II POW letter might be encrypted include a specific way of writing the date (5/1/42 instead of May 1, 1942, for example) and an underlined signature.

He said he would love to see more family members come forward with similarly coded letters. American intelligence officers used very similar strategies for their POWs in Europe, evidence of which might be sitting, forgotten, on a dusty closet shelf somewhere.

In December, a coded message discovered on the skeletal remains of a World War II carrier pigeon was allegedly deciphered by an amateur history enthusiast in Canada, NBC News reports. Experts, however, remain unconvinced.

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