the first ever mid-air refuelling of an unmanned aircraft was today successfully achieved by the navy 's x-47b drone .
the salty dog 502 vehicle is one of two unmanned carrier air vehicle demonstrators -lrb- ucas-d -rrb- on the x-47b program .
earlier today , it plugged its in-flight refuelling -lrb- ifr -rrb- probe into the hose of an omega air kc-707 tanker off the coast of maryland .