EARLY IN THE Vietnam war, American forces identified 27 vital infrastructure targets in North Vietnam. The first 26 were destroyed from the air. The 27th—the Thanh Hoa bridge, known as “Dragon’s Jaw”—proved a tougher nut to crack. Only after five years, nearly 900 sorties and 11 lost planes did the Americans smash the bridge, recounts Michael Spencer, an Australian air-force pilot, in a study published in 2019.
It took a new breed of weapon: the laser-guided bomb, which had the added benefit of allowing pilots to stay at a safer distance and altitude from their targets. In a recent working paper, Lauren Kahn and Michael Horowitz, both of the University of Pennsylvania, examine how and why smart bombs, as they became known, spread across global arsenals (the study excludes other precision-guided munitions, such as missiles).
Having pioneered the first laser-guided bomb, the Paveway, in Vietnam, America made another leap in smart-bomb technology in the late 1990s. The joint direct attack munition (JDAM), a small kit that could be attached to older dumb bombs, used signals from GPS satellites rather than lasers to guide the bomb to its target. During the war against Iraq in 1991, less than 8% of the munitions used were guided; when America returned to that country 12 years later, over 67% were precision-guided in one form or another, most of them gravity bombs.
America’s allies and rivals, having watched the annihilation of Saddam Hussein’s forces in 1991, rushed to follow. In 1990 just nine countries had smart bombs; powers such as China, India and most NATO states lacked the capability. A decade later 22 possessed them. By 2017 the figure was 56 (see map). Ms Kahn and Mr Horowitz point to several factors that explain the pattern of that spread.
Unsurprisingly, high levels of internal and external threat, relative wealth and technological proficiency all play a role. Israel, for instance, which views itself as an embattled country in a sea of enemies, and has advanced civilian and defence industries, produces no fewer than 11 different types of smart bomb and imports another six types from America—the most diversified arsenal apart from America’s own.
Yet other factors are also at work. Democracies are more likely than autocracies to acquire smart bombs, even when controlling for other variables. One reason for that, suggest the authors, is that politicians in democracies are more sensitive to public opinion at home and criticism abroad, and thus under greater pressure to reduce collateral damage when waging war.
In practice, though, more precise weapons have not always resulted in a clinical form of warfare. In his study of the Battle of Mosul in 2016-17, in which an American-led coalition fought to regain control of Iraq’s third-largest city from Islamic State, Amos Fox, a major in the US Army, observed a “precision paradox”. Highly precise strikes often failed to kill all the fighters in a building, causing them to flee to another building, which would then be struck again—and so on. “This paradoxical targeting loop generated a spidering effect,” wrote Major Fox. Over 10,000 civilians were ultimately killed in Mosul, about a third of them by the coalition. “In most cases...over-reliance on [precision strikes] increased death and collateral damage during the battle,” he concludes.