I longed to have a real fight against an unknown opponent.

I always felt awkward going into a fight with an unknown opponent.

This was a far more difficult and dangerous thing to try against an unknown opponent.

Hill was no coward but he didn't like fighting against unknown and invisible opponents.

The powers of Nature are on the side of the unknown opponent.

Almost at the same moment he noted on the viewscreen that his unknown opponent was going into an attack position.

The unknown opponent answered with a burst of machinegun fire.

With no further prompting, Pias began the ship on its course toward the unknown opponent.

It was no longer fighting in the dark against a largely unknown opponent.

He parried it, however barely, and directed a thought at his unknown opponent.