NEW YORK – In the spring of 1798, Napoleon was assembling a naval fleet off the South of France, ready to sail for battle against the British.

The British, under the command of Adm. Horatio Nelson, had one question: Where was he headed?

Turkey, Ireland, Malta and Britain itself were all possibilities. But before the invention of satellite photographs or radio transmissions, Nelson had only his instincts – and some undependable intelligence – on which to rely.

Communication was so poor that at one point four separate British forces searched in vain for both Napoleon and each other. Nelson needed three months to find the French leader, tracking him down in Egypt and clashing in the famed Battle of the Nile.

“Until the coming of modern technology, it was bafflingly laborious to gather intelligence because you had to look for it at the speed of human movement,” says military historian John Keegan, author of “Intelligence in War: Knowledge of the Enemy From Napoleon to Al-Qaeda,” which has just been published by Alfred A. Knopf.

“Nelson would receive information saying the French had been at such and such a place a week ago. So he would have to send someone there to find out or go look for himself. Whatever you learned was often outdated.”

Keegan cautions that intelligence is no replacement for military strength – “Victory is … bought with blood rather than brains,” he writes. But curiosity, along with courage, has long marked the great leader.

As a young man in the Macedonian court, Alexander the Great was known for his thorough questioning of visitors from foreign lands. By the time he was conquering some of those lands, he had the unbeatable combination of military strength and local insight.

Through the 18th century, armies depended on ingenious, if primitive methods. “A generalized cloud of dust usually signified that the enemy foragers were about,” observed one military expert. “Dense and isolated towers of dust showed that the columns were already on the march.” A French official, Marshal de Saxe, surmised that the angle of reflected sunlight off an enemy sword could tell you whether it was advancing or in retreat.

The art of intelligence, Keegan notes, is not just in acquiring it, but in sharing it. Lord Nelson’s hunt for Napoleon would have been easier had it taken place three years later, after the publication of “Telegraphic Signals or Marine Vocabulary,” by naval expert Home Popham.

Before then, if a ship wanted to communicate with another ship, it had to approach close enough so that the commanders could speak. Popham developed a numeric code that allowed the British to transmit messages from afar. A series of numbered flags relayed the system’s most famous signal, “England Expects That Every Man Will Do His Duty,” which marked the opening of the victorious 1805 Battle of Trafalgar against Napoleon.

By mid-19th century, the Industrial Revolution had taken off and Civil War leaders were starting to communicate by telegraph instead of hand-delivered messages. But armies still relied on old-fashioned methods of acquiring knowledge. For the South, an unlikely asset was Jedediah Hotchkiss, a former schoolmaster hired by Gen. Stonewall Jackson to draw up maps for Virginia’s Shenandoah Valley.

Maps at the time were often old and inconsistent, with roads and towns assigned two or more names. Hotchkiss was not trained as a cartographer, but he had the sense to ride out himself on horseback and survey the terrain. His work, while crude by today’s standards, was far superior to the maps held by Northern commanders, enabling Jackson to more easily locate mountain gaps and river crossings.

Meanwhile, scientists in Europe were experimenting with what marked the next great advance in intelligence gathering: electromagnetic waves. While telegraphs required the installation of cable lines, a clumsy process at best during wartime, electromagnetic waves could be relayed through the air between communication centers.

Perfected by Gugliemo Marconi, wireless transmission radically changed the intelligence process, enabling speedy, long-distance communication.

As technology advanced through the 20th century, so did methods of tracking military foes. Aerial reconnaissance was in place by World War I, when Allied pilots could see German troops advancing on Belgium; computers emerged by the end of World War II.

Devices for intelligence have proliferated in the past 50 years: underwater sensors, space satellites, surveillance balloons, enough to make the adventures of Mata Hari and other spies seem romantic and obsolete.

But sophistication doesn’t equal certainty, as demonstrated by the current disputes in Iraq over everything from evidence of weapons of mass destruction to who is behind the recent wave of suicide attacks in Baghdad. Keegan also wonders whether electronic systems can help in the war against terrorism, noting that Al-Qaeda proved so effective at concealing its planning of the Sept. 11, 2001, attacks.

“Cryptology is now so good that you can’t read the enemies’ messages quickly enough for the information to be useful,” he says. “It might be months and months before you decipher the code.”

After Sept. 11, many in the United States criticized the lack of Arabic speakers in the intelligence community, saying that intercepting e-mails and wiretapping phone conversations were no substitute for firsthand observation.

Keegan agrees that the future of spying may lie in its pre-electronic past, in people, what the intelligence community calls humint (human intelligence). He even suggests an unlikely source for learning more about the process: the spy novels of such authors as John le Carre and John Buchan.

“The secret world has always occupied a halfway house between fact and fiction, and has been peopled as much by dreamers and fantasists as by pragmatists and men of reason,” Keegan writes.

Copy the Story Link