The screen beauty who invented spread spectrum

Often called "the most beautiful woman in films", Hedy Lamarr was not only a beautiful and talented actress but an innovative and intelligent inventor. She proved this by co-inventing spread spectrum technology.

Born Hedwig Eva Maria Kiesler in Vienna in 1914, she went to Max Reinhardt's acting school in Berlin during her late teens, and in 1933 she was the first actress to appear nude in a major film.

Fritz Mandl, Lamarr's first husband, was an arms manufacturer and while hosting dinner parties for Nazi officials, Hedy absorbed an education in munitions manufacturing. But disturbed by Mandl's arms sales to the Nazis, she escaped to London in 1937.

It was later said that she gained her knowledge of radio guiding systems by learning from Mandl.

In London, Hedy met film mogul Louis B Mayer, who took her to Hollywood and in 1940 she met George Antheil, experimental music pioneer with player pianos.

Finding they had a common hatred of Nazis and knowing that whoever controlled the Atlantic would win the war in Europe, they merged their ideas for radio-controlled torpedoes that would solve the problems of unpredictable ocean currents and evasive action by target ships.

They began talking about radio control for torpedoes. The idea itself was not new, but her concept of 'frequency hopping' was. She brought up the idea of radio control and Antheil suggested a device by which synchronisation could be achieved.

He proposed that rapid changes in radio frequencies could be coordinated the way he had coordinated the 16 synchronised player pianos in his film music Ballet Méanique.

He laid out a system based on 88 frequencies, corresponding to the number of keys on a piano, using perforated paper rolls which would turn in sync with one another, transmitting and receiving ever-changing frequencies, preventing interceptance and jamming.

Anticipating the US entry into the war, this invention could potentially protect US radio-guided torpedoes from Nazi interception because the enemy could neither deflect the torpedo nor produce a radio transmission to jam it.

Lamarr and Antheil worked on the idea for several months and then, in December 1940, sent a description of it to the National Inventors Council, which had been launched with much fanfare earlier in the year as a gatherer of novel ideas and inventions from the general public.

Its chairman was Charles F Kettering, the research director of General Motors. Over its lifetime, which lasted until 1974, the council collected more than 625,000 suggestions, few of which ever reached the patent stage.

According to Antheil, Kettering himself suggested that he and Lamarr develop their idea to the point of being patentable. With the help of an electrical engineering professor from the California Institute of Technology the patent was granted on 11 August 1942.

It specified that a high-altitude observation plane could steer the torpedo from above.

Despite the enthusiasm that Antheil said Kettering expressed, others were sceptical. One examiner at the Inventors Council doubted the clockwork mechanism that moved the perforated tape could be accurate enough.

The Navy turned its back on the invention, concluding that the mechanism would be too bulky to fit into a torpedo.

But in 1957, the concept was taken up by engineers at the Sylvania Electronic Systems Division, in Buffalo, New York. Their arrangement, using electronics rather than piano rolls, ultimately became a basic tool for secure military communications.

It was installed on ships sent to blockade Cuba in 1962, about three years after the Lamarr-Antheil patent had expired.

Subsequent patents in frequency changing, which are generally unrelated to torpedo control, have referred to the Lamarr-Antheil patent as the basis of the field, and the concept lies behind the principal anti-jamming device used today, for example, in the US government's Milstar defence communication satellite system.

In the 1960s, the technology was renamed spread spectrum.

Today, spread spectrum is used in:

• Mobile phones;
• Pagers;
• Wireless internet;
• Garage door openers;
• Traffic signals;
• Cordless phones;
• Helmet-based communications;
• Milstar defence satellite;
• Battlefield combat identification system.

"It is gratifying to see how an idea born more than 50 years ago during wartime is being used today to help people communicate in countries around the world," said Hedy.

She died in 2000.