Churchill called the thousands of puzzle-solvers and clerks who spent World War II at Bletchley Park secretly breaking enemy codes “my geese that laid the golden eggs and never cackled.”

And almost as extraordinary as their work was — some say the decryption of Germany’s Enigma machine hastened the end of the war by as many as two years — their loyalty to the Official Secrets Act is almost impossible to fathom. Codebreakers kept silent about their war effort for decades; the British government didn’t officially recognize Bletchley Park veterans until 2009. Nowadays, it is still possible to read newspaper obituaries of 90-year-olds who never told their spouses, parents or siblings what they really did during the war.

“The Bletchley Circle,” a three-part series that begins Sunday on PBS, finds an imaginative way to give overdue credit to those unrecognized government servants, most of whom were women.