Pirius quickly learned there was more to it than simple trench-hopping. The cadets had to consolidate and reinforce the trenches they found themselves in. And they practiced leapfrogging, in which a second line of troops would pass through the first to make a more rapid advance.

It got more complicated still. Platoons of ten apiece were clustered into companies of maybe a hundred warm bodies. They practiced maneuvering as a company, in which one platoon would advance under the covering fire of another, all the while keeping the line intact. The next level up was a battalion, in which a thousand cadets would wash forward in coordinated waves. The instructors would throw unexpected problems in their way, and the cadets learned how to accommodate holes appearing in their lines, or being forced to back up from unexpectedly fortified positions. The cadets did this over and over, until every one of them knew what was expected in any given situation.

These elaborate maneuvers were all about mutual protection. Each company was covered by those to either side of it, just as each platoon was protected through mutual cover by the fellows down the line—which was why it was so important to keep the line together.

But for an individual trooper, in the end your only real protection was the presence of those around you, in your own platoon. You had to rely on them to watch your back—and if the worst happened, you had to hope that one of them would take the hit that might otherwise have taken you out.

The cadets seemed to understand that. If you were stuck in your skinsuit on a Rock falling into Xeelee fire, the great sweeping strategy of the war meant little. You were there to fight for your comrades. Very close bonds formed between the cadets—bonds that were strictly non-Doctrinal, as you weren’t really supposed to have loyalties to anything but the greater cause. But the instinct to fight for your comrades seemed as deep as humanity itself. It couldn’t be denied—indeed it had to be encouraged, quietly, whatever the Doctrines preached.

Pirius tried not to think about his situation. He knew he wasn’t here to think. But there were obvious questions he couldn’t help asking. For instance, why use human muscles to dig when you could get machines to do it for you?

He heard a whole series of rationales. Even after millennia of development it was difficult to shield equipment from the blistering radiation environment inside the Mass. Machines were liable to break down—and of course they drew the fire of the Xeelee. Humans were comparatively robust, at least for a while. Then there was the psychological factor: the trenches and foxholes were there to provide cover for the infantry, and nobody trusted a trench dug by a machine as much as one you dug out yourself. It was good for morale, then, to keep digging, digging.