Lifeguards in Australia used a drone to rescue two swimmers from drowning this week, the first such rescue in the world, according to local government.  Two teenagers were caught in a rip tide at Lennox Head, a coastal town in northern New South Wales.  On the beach, someone saw their struggle, and alerted lifeguards.  As it happens, they were just then in training with the drone, called a Westpac Little Ripper Lifesaver.  Supervisor Jai Sheridan piloted the unmanned craft to drop an inflatable pontoon.  Holding the device, the swimmers returned to shore unharmed.  Deployment took just one or two minutes, Sheridan reports, faster than a traditional rescue.