In the mid-1990s, someone at the Pentagon came up with a novel solution to a vexing problem: how to shoot down enemy missiles when they are most vulnerable, well before they approach their targets. The answer: Mount a powerful laser on a modified Boeing 747 that can zap missiles in their boost phase, when they are slowly lifting off and laden with fuel.

The Airborne Laser was eight years behind schedule and $4 billion over budget when then–Defense Secretary Robert Gates decided that the whole notion of a 747 flying lazy circles in the skies near a potential adversary, waiting for a possible missile launch, was prohibitively expensive and totally impractical.

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