And when the action began its terrible grinding, the Service Corps became field medics and stretcher bearers. Infantry skinsuits were designed to keep you alive as long as possible, but they were primarily fighting armor, and traumatic injuries would be beyond any suit’s capacity to stabilize. Pirius was taught how to apply the simple medicine possible through a skinsuit, such as tying off a damaged limb. And he learned how to bundle a body, locked in a rigid suit, onto open-frame stretchers, and to crawl with casualties through the earthworks back to casualty clearing stations.

So as Service Corps, they would be exposed to fire just as much as the frontline fighters, if not more so. Not that that gained them any respect from the frontliners, who seemed convinced that the Service Corps had it soft, with the first pick of rations, unlimited benefits, and protection from the battle.

There were a few other Navy exiles, like Pirius, and other undesirables in the Service Corps. But most of their number was made up of infantry troopers who had managed to survive one or two actions and grown too old, or perhaps too wounded or shocked, to fight anymore. These superannuated misfits felt misunderstood and put-upon. As they worked, they would sing their own plaintive song: We are the ASC / We work all night, we work all day / The more we work, the more we may / It makes no difference… Few of these gloomy veterans were older than twenty.

Eventually they were introduced to more sophisticated surface operations.

The cadets were taught to move in the open. They were organized into platoons of ten, which practiced moving together. The basic technique was to advance through lines of trenches toward an enemy position. You scrambled out of one trench, running or crawling across the asteroid dirt, and then hurled yourself into the next. The instructors used drone bots to simulate enemy fire — cadets would be “killed” by laser spots that made their suits go rigid. The inertial belts were priceless; without them the simplest kick or misstep could send you floating upward — but of course you also practiced how to keep moving forward even if your belt failed. The cadets seemed to enjoy this running around, apparently not imagining how it would be to go through this in combat conditions.

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.

But his pilot’s training prompted more questions. Why stick to such a crude strategy? Even using ground troops you could imagine more subtlety. You could coordinate your forces, strike with precision, move on.

He wasn’t about to ask such questions of Captain Marta, but, soaking up his training, he could figure out what the answers would be. A Rock offered shelter, so you had to stick to its ground. But in combat a Rock was drenched in firepower — and, even if the Xeelee didn’t show up to play, in the hard radiation of the Core. You couldn’t rely on communication, coordination, in such circumstances; you had to train for a worst case, in which every platoon, maybe every trooper, was cut off from everybody else, save for what she could see of the battlefield around her. In this ultimate war, only the crudest of tactics could be relied on to work.

But, guided by his conversations with This Burden Must Pass, he began to suspect that the truth behind the strategy was ideological. Clinging to humanity was the essence of the Druz Doctrines, the principles that had kept mankind united across twenty thousand years and the span of a Galaxy. So humans had to wage this war, humans had to dig their trenches, and fight and die, not their machines.

Pirius built up a new image of the Front in his head. It was a great shell enclosing the center of the Galaxy, and it was studded with worldlets like this one, and on every one of them there were human beings, digging and burrowing. They were digging for victory; that was what the instructors told them. And whether or not they ever achieved that victory, Pirius thought, with every spadeful of glistening asteroid dirt, the Druz Doctrines and the unity of mankind were reinforced that little bit more.