The U.S.-led air campaign against Islamic State militants in Iraq and Syria is having a devastating effect on the insurgent forces. That is, if you believe the Pentagon's continuing tally of destroyed and damaged vehicles, facilities and troop formations.

But the official statistics are meaningless. Because U.S. pilots are flying blind. To a great extent, they don't know what — if anything — they're hitting.

More so than in any recent conflict, American aviators soaring over Iraq and Syria rely on remote-controlled drones to spot targets for them. This is one consequence of President Barack Obama's policy barring U.S. ground troops from any direct combat role.