FILE -- In this Feb. 12, 1991 file photo, U.S. Marines prepare to board Chinook CH-46 helicopters during a deployment exercise in the desert of Saudi Arabia during the Persian Gulf crisis. Twenty five years after the first U.S. Marines swept across the border into Kuwait in the 1991 Gulf War, American forces find themselves battling the extremist Islamic State group, born out of al-Qaida, in the splintered territories of Iraq and Syria. (AP Photo/Sadayuki Mikami, File)