The coalition airstrike that recently killed more than 100 civilians in Mosul underscores a familiar challenge of dense, urban warfare: how can the military more precisely hit targets from the air? Lasers represent the apogee of precision and the Pentagon has several ongoing programs that will reach readiness in the coming years. The head of Air Force Special Operations Command recently said that lasers should absolutely be "part of the discussion" about how to hit terrorists — but so should the significant legal and practical obstacles that remain.

The military already uses low-power lasers to guide its weapons, from missiles to small arms. But recent advances in solid-state fiber lasers have renewed Pentagon interest in high-energy weapons that might do the damage by themselves, firing from everything from trucks to experimental helicopter drones.