Background

Intelligence

Collecting information about a (potential) foe's capabilities (economic, military) and intentions (political, military)
As old as nations themselves!
New about the late 19th and 20th Centuries: rise of far-flung empires, increasing use of technologies for communications, need for command and control
Every measure has a counter measure, and in turn, a counter-counter measure!

To communicate is to reveal: communication methods lead to detection
Can the detector be detected? identified as to individual and location?
Can the interceptor be fooled? traffic analysis and deception?
Can the communicator be stopped from successfully communicating? jamming?
Can the communicator hide his/her communications? stealth?
Intelligence collection methods include: spying, reconnaissance, spy satellites, code breaking
Human intelligence (HUMINT) aka spies
Signal intelligence (SIGINT)/Communications intelligence (COMINT) often used interchangeable, especially up through WWII
Modern militaries use many forms of electromagnetic radiation that don't involve communications, but are used for detection (e.g., RADAR)
Information derived from the monitoring, interception, decryption and evaluation of enemy radio communications
Naval intelligence particularly important, as until the development of recon satellites, the ability to put "eyes" at sea was very limited!

A Little Physics: Electromagnetic Radiation

Rapid development of scientific understanding of the physical nature of electricity through the 19th Century
Electricity and magnetism are related forces
Maxwell's Equations (1866): electricity and light are related forces; other forces beyond these predicted to exist
Hertz (1888): demonstrates the ability to send "sparks" across a room--demonstration of radio waves
Marconi (1895}: development of the aerial, communications at greater distances, across the Atlantic (1901)
Electromagnetic radiation: wave length x frequency = constant (speed of light)
Shorter the wavelength, the higher the frequency, the more radio behaves like light (line of sight, cannot pass through walls)
Early very long wave transmission propagated long distances (e.g., across the Atlantic through the "ground wave" effect)
Paradoxically, short wave transmission propagates even better due to atmospheric "bounce" (e.g., Austrialia to Britain)
At Very High Frequencies (e.g., TV, FM Radio, Cell Phones) propagation limited to horizon (about 20 miles or less)
Moving to higher frequencies enabled the evolution of Wireless Telegraphy (on/off) to Radio Telephony (modulation of human voice)
Higher frequencies also mean shorter wavelengths, smaller aerials, smaller transmitters and receivers, greater portability
Ship-to-ship, ship-to-shore, ground-to-air communications
Higher frequencies make radio of interest to ground forces!
Early days, tuning to specific frequencies is difficult--mutual interference common--origin of military use of jamming?
Huge shore-based transmitting stations, multiple football fields in size, transmitting a huge power
Since anyone with a receiver with the right capabilities could "tune in", the importance of cryptography comes to the fore!

Radio communications/telephony/cryptography
Radio direction finding
Traffic analysis: increasing tempo of radio traffic could indicate an upcoming operation OR an attempt at deception

Page last modified 28 January 2003, by Randy H. Katz, randy@cs.Berkeley.edu