Free Camouflage by Joe Haldeman

perfectly.
    “Good.” He wheeled and marched back toward the door. “You shitbirds didn’t see nothin’. Get to sleep. Formation at 0500.” He snapped off the lights.
    After a minute of silence, people started to whisper. The changeling sat upright in its bunk. Someone brought him aspirin and a cup of water.
    “Where’d you learn to fight like that?”
    “Fell out of bed,” it said. “So did the sergeant.”
    That was repeated all over the camp, especially when the next morning they had a new drill sergeant, and the old one was nowhere to be seen. They gave the changeling the nickname “Joe Louis.”
    The new drill sergeant was not inclined to single out Joe Louis. But he didn’t favor him, either. He had eight weeks to turn all these pathetic civilians into Marines.
    For the first week they did little other than run, march, and suffer through calisthenics, from five in the morning until chow call at night—and sometimes a few more miles’ run after dinner, just to settle their stomachs. The changeling found it all fairly restful, but observed other people’s responses to the stress and did an exactly average amount of sweating and groaning. At the rifle range, it aimed to miss the bull’s-eye most of the time, without being conspicuously bad.
    It almost made a mistake at the gas-mask training “final exam.” One at a time, the recruits were led into a darkenedroom where they had to wait until the gas-masked sergeant within asked you for your name, rank, and serial number. You gasped them out and then quickly put on your gas mask, saluted, and left.
    The changeling walked into the dark room and took a breath, and was almost overcome with an inchoate rush of nostalgia. It had forgotten, after a million years, that its home planet’s atmosphere was similar to this, about 10 percent chlorine. The smell was delightful.
    The sergeant with the gas mask and clipboard let it wait for about two minutes. Then he turned a bright flashlight into its eyes. “Are you breathing, Private Berry?”
    “No, sir.”
    “Don’t call me ‘sir’; I work for a living.” He kept the flashlight steady for another minute. “I’ll be goddamned. You swim a lot, Private Berry?”
    “Yes, Sergeant.”
    “Underwater, I guess?”
    “Yes, Sergeant.”
    He paused for another thirty seconds and shook his head. “ Dang! Give me your name, rank, and serial number, and put the mask on.” The changeling did. “Now get the hell outta here before you puke all over me.”
    The changeling went through the door where the EXIT sign glowed dim green, enjoying the last whiff of chlorine trapped inside the mask.
    Outside, twenty men were sprawled around in various attitudes of misery, coughing and retching. There were spatters and pools of vomit everywhere. The changeling ordered his stomach to eject its contents.
    A friend, Hugh, came over to where he was kneeling and pounded him on the back. “Geez Louise, Jimmy. You musta held your breath three minutes.”
    The changeling coughed in what it hoped was an appropriate way. “Swim a lot underwater,” it said breathlessly. “God, don’t that stuff smell awful?”
    But the memory of nostalgia was strong. Where on Earth could it have lived, where chlorine was so concentrated in the air? Nowhere on the surface. That would be a good research project, after the war.
    A lot of their training had a quality of improvisation, since much of the material of war had already left for the Pacific. So they learned how to work with tanks by advancing in formation behind a dumptruck carrying TANK signs wired to its front and rear. They carried World War I Springfield rifles and practiced with them on the range.
    Hand-to-hand combat training was a ballet of restraint for the changeling, who had been a remorseless predator for most of its life. It allowed the other trainees to throw it around and simulate dangerous blows. When it was its turn to be aggressive, it spared everyone’s lives, knowing it could