They are up to 300 ft high, slow moving but in the early stages of the war, invulnerable to human weapons. They are armed with an energy shield, a devastating energy cannon, and surrounded by clouds of poisonous gasses that mirror the atmosphere of their pilots’ home world. What is inside each Heron is unknown at first, but it’s clear that they can lay waste to the great cities of Europe in a matter of days, and also that they act as the hub for battalions of smaller tripod war-machines, that the troops have christened 'Spiders'