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FOR AS long as Tony Loder can remember, he鈥檇 known that his mother, Hedy
Lamarr, was a film star. But at seven years old, he suddenly discovered that she
had an amazing secret locked away in her past. Not the usual Hollywood fare of
sex, booze or drugs鈥攈is mother鈥檚 secret was far more remarkable. 鈥淲e were
going through some old boxes in the attic,鈥� he recalls, 鈥渨hen she suddenly
pulled out some old papers and said `Oh yes, I invented radio-guided
torpedoes.'鈥� Loder was too young to see anything weird in this at the time, but
decades later, it seem very different. 鈥淪he was twenty years ahead of her time,鈥�
he says.

But Lamarr did more than simply invent a way of controlling torpedoes. In
1941, with avant-garde composer George Antheil, she was granted US patent number
2 292 387 for a 鈥淪ecret Communication System鈥� that used a new technique to
conceal a radio message by sprinkling it across a wide range of frequencies.

With a simple mechanism based on the insides of a player piano, messages
would jump or 鈥渉op鈥� from one frequency to another at random, making it almost
impossible to listen in or to jam the signal. Lamarr intended that the system
would steer a torpedo remotely, guiding it towards a moving ship with no danger
of interference from the enemy. Today, the technique they proposed鈥攏ow
called frequency hopping spread spectrum鈥攍ies at the heart of the latest
communications systems, the revolution in mobile phones and could soon offer
cheap wireless access to the Internet.

Their design overcame one of the biggest weaknesses of radio communications.
Normally, radio signals鈥攖he sort used for broadcasting music, for
instance鈥攁re transmitted in a narrow frequency band and picked up by
carefully tuning the receiver to the same band. Unfortunately, this method is
useless for sending secret communications: anyone can listen in, and worse, the
signal is easily lost in the fuzz of background noise or can be blocked
completely by a devious enemy.

Lamarr first learnt of the vulnerability of radio signals in the 1930s while
she was married to Fritz Mandl, an Austrian arms dealer. Mandl was selling
bombs, bullets and torpedoes to the rapidly expanding military forces of Germany
and Italy鈥攁nd was also keen to show off his beautiful young wife. Possibly
to improve his chances of making a sale, she sat in on many of his meetings,
where she heard that Mandl鈥檚 torpedoes often missed their target. What navies
really wanted, she learnt, was a way to guide a torpedo as it raced through the
water. Radio control fitted the bill, but if a torpedo relied on a single
frequency, the control system could easily be jammed.

After four years of marriage, Lamarr left her domineering husband, met
director Louis B. Mayer and travelled to Hollywood for a new career in films.
According to Robert Price, an electrical engineer and spread spectrum historian,
Lamarr was staunchly anti-Nazi. 鈥淪he wanted to bring a weapon across the
Atlantic to use against Hitler,鈥� he says. In the US, she came across the
push-button radio. 鈥淪he knew if you pushed a button, you changed the radio鈥檚
frequency,鈥� Price says. 鈥淭hat got her started on the idea of frequency
丑辞辫辫颈苍驳.鈥�

Steering a torpedo with a signal that hopped frequencies seemingly at random
would make the signal unjammable. Enemy radio operators scanning across the
airwaves would hear no more than a fragment of the signal in their headphones
before the transmission hopped to another frequency and disappeared into
background noise.

To work, both receiver and transmitter must 鈥渉op鈥� in perfect synchronisation.
This is where the innovative composer George Antheil came to Lamarr鈥檚 aid. The
couple met at a Hollywood party and when Lamarr told Antheil about her idea, it
turned out that he had already solved the synchronisation problem.

Sixteen years before, he had composed Ballet Mechanique, a musical
piece written for aircraft propellers, wooden rattles, tin gongs and four
synchronised player pianos. Antheil鈥檚 mechanical music made quite an impression:
one reviewer described it as if 鈥測ou were to listen to the notes of circular
saws biting their way through steel, mixed with the crash of a steel die plant鈥�.
Crucially, the pianos used synchronised motors to drive matching paper rolls
punched with holes to indicate when the pianos should play a note.

Antheil and Lamarr realised a transmitter and receiver could be synchronised
in the same way. In their patent, the transmitter and torpedo each contained a
paper roll punched with an identical pattern of random holes, a motor and
mechanical switches. As the torpedo was launched, the motors would drive the
rolls and the holes in the paper would change the frequency settings of both the
transmitter and receiver in much the same way that a push-button radio changes
radio station.

Impossible task

The position of the holes determined the frequency of the signals, and their
length controlled the delay between hops. And enemy eavesdroppers would find it
almost impossible to monitor this broad range of frequencies at the same
time.

The pair gave their invention to the US government but despite its
advantages, frequency hopping spread spectrum wasn鈥檛 used during the Second
World War鈥攑erhaps the components were too heavy or maybe the US Navy
disliked the thought of paper rolls inside their shiny torpedoes. Instead, the
system was reinvented independently years after the war and miniaturised using
transistors.

Today, frequency hopping technology is used in the US Milstar military
communications system, and in mobile phone systems too. Since it relies on many
frequencies, callers can share the same frequencies without their messages
interfering with each other. Other uses are appearing all the time: in
interactive television transmission, wireless access to the Internet and for
sending data along power lines, for instance.

Lamarr鈥檚 and Antheil鈥檚 patent was, according to Price, 鈥渢he generic
invention鈥攖he first in the field鈥�. But recognition has been slow to
arrive. They received an Electronics Frontier Foundation 1997 Pioneer award and
Loder recently accepted the Victor Kaplan medal for invention from the Austrian
Academy of Sciences on his mother鈥檚 behalf.

Honour has come too late for Antheil鈥攈e died in 1959. But from her
house in Florida, Lamarr still follows the development of their idea with
interest. In a world with all too few scientific heroines, many now believe her
contribution should be universally recognised. 鈥淪he is the Marie Curie of spread
spectrum,鈥� says Price. Loder agrees: 鈥淭here鈥檚 no equivalent,鈥� he says. 鈥淟et鈥檚
see what Mel Gibson鈥檚 going to give us.鈥�