How does Paul describe the enemy infantry?

From the text:

We do not see the guns that bombard us; the attacking lines of the enemy infantry are men like ourselves; but these tanks are machines, their caterpillars run on as endless as the war, they are annihilation, they roll without feeling into the craters, and climb up again without stopping, a fleet of roaring, smoke-belching armour-clads, invulnerable steel beasts squashing the dead and the wounded--we shrivel up in our thin skin before them, against their colossal weight our arms are sticks of straw, and our hand-grenades matches.