Julia Parsons, a U.S. Navy code breaker during World War II who was among the last survivors of a top-secret team of women that unscrambled messages to and from German U-boats, died on April 18 in Aspinwall, Pa. She was 104.

Her death, in a Veterans Affairs hospice facility, was confirmed by her daughter Margaret Breines.

A lover of puzzles and crosswords while growing up in Pittsburgh during the Great Depression, Mrs. Parsons deciphered German military messages that had been created by an Enigma machine, a typewriter-size device with a keyboard wired to internal rotors, which generated millions of codes. Her efforts provided Allied forces with information critical to evading, attacking and sinking enemy submarines.

The Germans thought their machine was impenetrable. “They just refused to believe that anyone could break their codes,” Thomas Perera, a former psychology professor at Montclair State University who collects Enigma machines and has an online museum devoted to them, said in an interview. “Their submarines were sending their exact latitude and longitude every day.”

The unraveling of the Enigma puzzle began in the late 1930s, when Polish mathematicians, using intelligence gathered by French authorities, reverse-engineered the device and began developing the Bombe, a computer-like code-breaking machine. The Poles shared the information with British authorities.

In 1941, during an operation that was among the war’s most closely held secrets, the Royal Navy captured a German submarine with an Enigma machine on board. The British mathematician Alan Turing — working secretly with intelligence services in England — used it to refine the Bombe. British authorities sent instructions for building the Bombe to the U.S. Navy.