ELMENDORF AIR FORCE BASE, Alaska — The Alaska National Guard said a US military cargo plane crashed at Elmendorf Air Force Base in Anchorage on Wednesday evening.Alaska National Guard spokesman Maj. Guy Hayes confirmed the crash of a C-17 plane.No other details were immediately available, including whether there were casualties.Anchorage Fire Dept. Captain Bryan Grella said his crew was just getting done with dinner around 6:30 p.m. local time at the downtown fire station when something caught his eye."It was a big, gray plume of smoke, and I saw a fireball go up in it," he said.