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Douglas Waller has specialized in histories of American intelligence operations from World War II forward — until now, with “Lincoln’s Spies.”

In the new book, Waller looks backward more than a century and a half to write about intelligence operations in the Civil War. Toward the book’s end, he asks:

“What role did intelligence play in this conflict? More than was acknowledged at the time. Northern and Southern civilian leaders largely neglected the gathering of political and economic intelligence because they knew the other’s politics, geography, and economic wherewithal. Each side’s generals had been classmates in the same military academies and had fought together. They often showed disinterest in strategic and tactical intelligence, believing they could already foresee how an adversary they had known for years would react on the battlefield. But the work of Lincoln’s spies — even his inept ones like Pinkerton, his corrupt ones like Baker, and particularly his best ones like Sharpe and Van Lew — made a difference.”

The Sharpe that author Waller cites was George Sharpe, intelligence chief for Gen. Ulysses S. Grant and his two predecessors — Joseph Hooker and George Meade — on the Virginia front. The author outlines how that war’s intelligence worked by noting that in 1863, “Sharpe now had access to everything that came to Hooker’s headquarters — the reports from cavalry reconnaissance missions, Signal Corps stations, and balloons in the sky, the interceptions of Confederate flag messages, the newspapers from Richmond, the intelligence telegraphed from neighboring commands. Sharpe’s bureau then sorted, synthesized, and analyzed all the information to present to Hooker the clearest, most comprehensive picture of the enemy a Union commander had ever had.”

Although Civil War soldiers lacked almost all of today’s technology, Waller spends some time recalling the Union’s spy balloons, launched with observers aboard to peer deeper into Confederate lines. Think of the balloons as precursors to spy planes, drones and reconnaissance satellites. (Even so, the balloons were grounded for good just before the Battle of Gettysburg in 1863.)

Civil War buffs will delve into “Lincoln’s Spies,” feasting on details unearthed by Waller’s deep-digging research.

Harry Levins of Manchester retired in 2007 as senior writer of the Post-Dispatch.