British soldier John Pryor sent letters home to his family from a Nazi POW camp for five years during World War II. Seventy years later, they finally know what he actually wrote. A mathematician at Plymouth University has deciphered the coded messages hidden inside the innocuous-looking letters for the first time since the war, revealing Pryor was really asking for items to help him escape and reporting details of German military targets, the BBC reports.
The BBC explains that the code, which Pryor would have learned from British secret agents, involved taking the first letters of each word, translating those letters to numbers, and then translating the numbers back to letters. Deciphered, this sentence—"A few weeks ago we arranged a rather useful scheme, so men could get 'lager'"—reads "MAPS." The letters would have been deciphered at the time by British intelligence, but were then passed on to the family in their original form. "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," Pryor's son, John, told the Plymouth Herald. "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."