UFO crew (3)
(Another definition for ets that I've seen is " Who teach soldiers".)
'ufo crew' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aliens that I've seen before include "Outsiders" , "Extra-terrestrial beings" , "'Little green men'?" , "Strangers, extraterrestrials" , "Strange forms of life" .)