American troops deployed in Syria are increasingly having to defend themselves against Russian jamming devices—electronic attacks with potentially lethal consequences, according to U.S. military officials and analysts. Officers who have experienced the jamming—known as electronic warfare—say it’s no less dangerous than conventional attacks with bombs and artillery. But they also say it’s allowing U.S. troops a rare opportunity to experience Russian technology in the battlefield and figure out how to defend against it. “It’s a great opportunity for us to operate particularly in the Syrian environment where the Russians are active.” Daniel Goure, an expert on national security and military...