Hour of the Horde — Gordon R. Dickson

Aug 1978 mass market paperback, Gordon R. Dickson (The Dragon On The Border). Annihilating everything before it, a horde of monstrous space travelers were advancing through the stars. And Earth lay in their route. To defend their home planets, the worlds that lay in the path of the monsters created a super defense force, asking each planet to contribute one especially talented warrior to help turn the invaders away. - Goodreads