Hour of the Horde by Gordon R. Dickson:|
The Horde roved the galaxies, stripping whole star systems of life. As they advance on our galaxy, the Milky Way, a galaxy-wide force hastily arrayed to stop them. But Miles Vander, the warrior sent by Earth to join the defense, must first convince his alien crew/members that he is just as good a soldier as they.
Wolfling by Gordon R. Dickson:
Earth was a primitive outpost, its people dubbed 'wolflings' by the rulers of the galactic empire. Jim Kell was sent to the High-Born ruler's Throne World, with orders only to observe - until he cast away his orders from Earth and proved himself a Wolflinq indeed.
Gremlins Go Home by Gordon R. Dickson and Ben Bova:
Suppose that elves, gremlins, and leprechauns are really tiny aliens marooned on Earth for hundreds of years. They want to go home, and human technology finally can make it possible - if they can get aboard NASA's Mars rocket and hijack it! Pity the poor human who has to help them...