Disunion follows the Civil War as it unfolded.

The First Battle of Bull Run, like freshman year of college, was a time for earning reputations — and nicknames. On that same afternoon when Confederate Gen. Thomas Jonathan Jackson won his moniker, “Stonewall,” he bestowed an equally flattering reputation on a Union regiment called the 14th Brooklyn, which wore red wool trousers as part of their local militia uniform modeled after the French chasseurs. The 14th Brooklyn — the only regiment in the Union Army called by a city’s name rather than a state — was giving Jackson and his troops quite a time on Henry House Hill, and at some point Stonewall braced his soldiers for yet another charge by shouting “Hold on Boys! Here come those red-legged devils again!”

The nickname stuck, and thanks to generous funding from the Brooklyn home front, the pants did, too. While the Army phased out other unique garb in favor of standard blues, the 14th wore their red trousers for the length of their three-year enlistment, through ferocious battles like Antietam, Gettysburg, the Wilderness and Spotsylvania.

Not that any of this gets you a discount at a Ponderosa steakhouse in Falmouth, Va., where about 12 members of the unit dined on a recent Saturday night. These weren’t ghosts of soldiers past, of course, but re-enactors — including myself, dressed in red pants and smeared with mud — in town for a memorial dedication. Our hair was matted and oily from a night of camping and a day of marching; the women among us were armored in hoop skirts that required wide berth. Nevertheless, the residents of Stafford County were kind to us Yankees, just as they were for the most part in 1862 and 1863, when the Union Army camped along the Rappahannock River.

Re-enactors get good at straddling centuries, whether that means wandering the 21st in Civil War garb or receiving modern visitors to our 19th-century masquerades. That morning our latter-day revival of the 14th Brooklyn stood honor guard at Falmouth’s Union Church cemetery, part of the dedication ceremony for a historical marker honoring a former slave and the seven soldiers whose funeral he attended in April 1862. Afterward we answered questions and demonstrated musket-firing techniques for the several hundred locals and tourists who’d come out to see our encampment. Spectators tend to ask us the same things: Are those uniforms hot? (Yes.) Are you guys zouaves? (No.) The re-enactor’s challenge, I’ve learned, is to treat each conversation as a fresh performance.

I first met the men of the 14th Brooklyn in 2002, at the rededication of a monument in Green-Wood Cemetery. I had come out of curiosity, but soon struck up a conversation with Anthony Dellarocca, who, when he’s not carrying a musket, runs a limousine service in Lindenhurst, N.Y. Anthony was viscerally upset by the presence of a re-enactor portraying the wartime governor of New York, Edwin D. Morgan. The governor, he seethed, had tried to keep the 14th at home in the spring of 1861, but Col. Alfred Wood, the regiment’s leader, went to Washington and secured orders to muster from President Lincoln himself. Each of the dozen or so re-enactors at Green-Wood that afternoon had assumed the identity of an actual soldier from the 14th, and they were eager to tell me about the battles they had seen and the wounds they had sustained.

These re-enactors’ obsessiveness amused me, and then intrigued me, and then inspired me. By the time I left the cemetery, I was hooked, and for the next eight years I had the 14th Brooklyn stuck in the back of my head. I wanted to write a book about the regiment, but a different book (and a day job, and life) kept me from delving very deep into their story.

With the sesquicentennial on the horizon, though, I finally made the 14th a priority. But I didn’t want to spend all of my time in libraries. I wanted to get as close as I could to being there. I wanted to enlist. This April, almost exactly 150 years to the day after Lincoln’s famous call for volunteers, I borrowed some gear and came to Camp Wood, the 14th’s training weekend at Old Bethpage Village Restoration, on Long Island.

Most of my comrades, I would learn, lived in the island’s New York suburbs, though most had Brooklyn ties. (Frank Ruiz Sr., our captain, grew up in Bay Ridge.) I would be the first new recruit in a while to actually live in Brooklyn, and that weekend the veterans seemed concerned that this might not be the kind of activity a modern Brooklynite would enjoy. It was colder than usual, and we slept in canvas tents on hard ground. They made me march; taught me to move from two ranks to a column of four and back again; to load and hold a musket; to shoot on my feet, on my belly. The older guys kept checking in, asking how I was doing, whether I was enjoying myself.

I guess I was wary, too. I wondered what I was getting myself into, and who these men would turn out to be, once they’d donned their period selves. I’d read Tony Horwitz’s “Confederates in the Attic,” which is full of re-enactors as Southern eccentrics and obsessives. But the guys in the 14th aren’t haunted holdouts from a society that can’t forget. They are bridge-and-tunnel history buffs eager to educate a society that doesn’t remember. They are in their 60s, their 30s, their teens; there are father-son pairs; a butcher, a banker, a painter, a courthouse security guard. On the whole, they care more — and know more — about history than anyone I’d ever joined around a campfire.

We’re a tight group, but a lot of what we do is for the public. We stage actual battles along with other groups of re-enactors, and we conduct living-history events like the one at Falmouth. But we also do a lot of what you might call “nonspecific combat events” — essentially, getting together to indulge our inner infantrymen. Take Jesse Henry, a 28-year-old member of our regiment from Long Beach, N.Y. Jesse has developed a niche specialty at getting “shot.” I’ve seen Jesse go down three or four times in a single day of action, and he’s quite good. He’s not one to just get back up on his own, either; he prefers to be carried off the field as dead weight. In Falmouth, there had been no combat, and so when our formal duties were done, our lieutenant, Frank Ruiz Jr., put Henry out of his misery: Ruiz loaded his musket with powder, Henry took off running across a field, and Ruiz fired from some 40 yards away. Henry twisted into a contortion and slumped to the ground.

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Further lighthearted morbidity came around sunset. We drove over to the White Oak Civil War Museum, a modest old school building filled with installations and artifacts that amazed even the most-well-traveled buffs among us. For an hour we gawked at mounds of bullets, coins and buttons; shelves full of bottles, canteens and belt buckles. With the curator, D.P. Newton, we flipped through old binders of photocopied letters, reports, ledgers and photos. Then we went out back, where Mr. Newton had constructed several wood-and-canvas winter huts, complete with fireplaces and bunks. Frank Senior vowed to build one in his back yard. Nearby there were mock fresh graves, including an empty one, of which we quickly made use. Jerry Bergeron, a 51-year-old from Pennsylvania, stood in as a casualty, and the men lifted his limp body and laid him in the hole. Then he got back out and we went to Ponderosa.

Re-enacting, in other words, is a mash-up of camping, American history, Halloween and playing war. These boyhood pursuits, when combined, deliver an unexpectedly satisfying experience for an adult. We’re not that different from people who wear professional sports jerseys and play touch football in the front yard. We’re like the fans who bringing baseball gloves to Yankee Stadium, except we bring muskets to battlefields.

And I love it. I’ve gone camping in Green-Wood Cemetery on Memorial Day weekend, sleeping in a tent in the rain a mere mile from my own dry bed. I fought the sesquicentennial of the First Battle of Bull Run in 110-degree heat, even though I came down with heat exhaustion and had to decamp to an air-conditioned hotel room, mildly ashamed. I went to the desk clerk looking like hell and asked if I could bring a musket in from the car. This being Virginia, she said yes. I showered like a zombie and drank as much water as my stomach could handle. Just before collapsing in bed I set two alarms — one that would get me up early enough to fight the second day and one that would get me up early enough to watch. I woke up 10 hours later, an hour after the second alarm, and felt better, save for the pangs of regret for having missed Day Two of the misery.

As feeble as fleeing Bull Run made me feel, the hobby has toughened me up. I have a greater tolerance for being uncomfortable — hot or muddy or unshowered or poorly fed. And in a way I think it’s centering me. When we’re together in character, I’m following orders, I’m unplugged. Yes, when the public isn’t looking we sometimes sneak peeks at our “wireless telegraph” smartphones. And yeah, we go to Ponderosa in our uniforms. But even at its most inauthentic, re-enacting can be a meditation. When you’re in that hand-sewn wool uniform, in a muddy tent, swigging from a beeswax-sealed tin canteen and smelling like a sausage, it’s the 21st-century public that seems strange.

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Matt Dellinger is the author of “Interstate 69: The Unfinished History of the Last Great American Highway.” He is at work on a book about the 14th Brooklyn. Photograph by Gus Powell.