But it was hard to take any action against an invisible enemy.

The invisible enemy did not appear to have been hit.

Almost a million and a half people had become victims of the invisible enemy during this 2nd attack.

These were "our boys" and we began willing them on against the invisible enemy.

Our companies opened fire and worked toward the invisible enemy by means of short rushes.

She looked up at the sky, as though challenging her invisible enemy.

I walked rapidly along the beach, talking with the invisible enemy.

If your child has asthma, it can seem like you're fighting an invisible enemy.

His arms were held up in front of him as if trying to fend off an invisible enemy.

But who says when this war against an invisible, intangible enemy is over?