Night after night for the past six weeks, U.S. fighter jets have streaked into the muggy sky from this vast desert airfield, their afterburners spewing orange flames as they head north on bombing runs over Iraq and Syria.

The American presence at Al-Dhafra, which the Pentagon has not publicly acknowledged, is a vital part of the U.S.-led campaign against Islamic State militants: The base’s twin runways have launched more strike aircraft — including the Air Force’s most-sophisticated warplane, the F-22 Raptor — than any other military facility in the region.

On many nights, the American planes are accompanied by a wave of F-16 Fighting Falcons operated by the UAE’s air force. After the U.S. military, Emirati fighters have conducted more missions against the Islamic State since the air war began than any other member of the multinational coalition, often striking targets that are just as difficult and dangerous as those attacked by the Americans. […]