Just as the bow and arrow and the musket changed the game of war, so did the radio, and that critical fact leads a PBS special called The Codebreaker to a little-known American heroine named Elizebeth Smith Friedman.
The ability to transmit wireless signals to a remote location meant wartime commanders could instantly exchange information and thus implement strategies more quickly over a much wider area.
Intriguingly enough, this new communication system sent those signals and messages through the same air to which the enemy had access.
The trick was to send the messages so the enemy could not decipher them, and military operations soon turned encryption into a science.
This prompted enemies everywhere to look for ways of breaking the codes anyway, and it turned out that only a tiny handful of people had the mental agility to outthink the sophisticated systems.
Fortunately for the United States, one of those people was Elizebeth Smith Friedman, whose personal skill and ability to develop a whole codebreaking system enabled the U.S. government to smash first Prohibition mobsters and later wolfpacks of Nazi submarines.
Friedman's contribution receives its full due in The Codebreaker, an American Experience production that premieres Monday at 9 p.m. ET on PBS (check local listings).
This recognition feels especially important because it wasn't until decades after her death that the unsealing of classified files revealed the depth and value of her work.
In the ensuing years, while Friedman was struggling through a diminished old age, FBI chief J. Edgar Hoover was taking credit for her work.
That gives a melancholy end to a mostly upbeat and inspiring story, despite the tragic events around which it unfolded.
Elizebeth Smith was raised a Quaker but resisted a life in which a woman's only role was to marry and raise the children. She married William Friedman, and they did have two children, but she also found that, like her husband, she had a talent for cryptography.
They both went into the field, William working for the government at a much higher salary and Elizebeth becoming so good that a reluctant law enforcement establishment finally had to break down and, against all its instincts, hire a woman.
While she worked on and off in cryptography for years, developing systems to root out hidden messages, her big score came in the 1930s.
The government knew bootleggers and distributors of illegal alcohol were sending radio messages about their delivery schedules from offshore boats, but they couldn't crack the codes until Friedman came aboard.
Her work helped lead to the capture and imprisonment of, among others, Al Capone.
The stakes increased geometrically a few years later when the U.S. found itself unable to break the codes by which Germany was signaling its U-boats where to find and sink Allied shipping.
Friedman did it and also set up a system by which other U.S. cryptographers could do the same. The first institutional codebreaking departments were built on the fundamentals of her system, which remain in use today.
Like all military personnel working in classified areas, Friedman signed a strict vow of silence regarding any information involving the project. Following that pledge, she never publicly spoke of her work during her lifetime.
The Codebreaker includes some technical material on the science of deciphering messages. It does not plunge in so deeply that any of the material becomes white noise to civilian viewers.
The Codebreaker also does not sensationalize Friedman's life. She is portrayed as a rebel with a cause, but not a fiery rebel. She had a long marriage that seems happy despite the intense pressure both she and William often found themselves under. If she rarely received proper credit for her work, she knew its value.
Because so much time has lapsed, The Codebreaker doesn't have the luxury of interviews with contemporaries, mostly relying instead on historians. They make our debt of gratitude clear.