Desmond Nunn, left, Yvette Lu and Jacob Guzman, three of the swing performers in the touring company of “Hamilton,” now at the Kennedy Center. (Marvin Joseph)

One of the most demanding roles in “Hamilton” is one you probably won’t notice: that of the “swing,” a performer who is prepared to play multiple parts in the show, sometimes with only a moment’s notice.

“I have to be ready at the drop of a dime to go onstage, and I have seven tracks in my head,” says Jacob Guzman, 23. “You’re always on the edge of the seat, not sure what’s going to happen tonight.”

Guzman was still memorizing his responsibilities as the touring company that’s now at the Kennedy Center launched last year in San Francisco. Mid-show, he was told he’d have to step in.

“You have to act like you know what you’re doing,” says Guzman, whose twin brother, David, is a swing in “Hamilton” on Broadway. “You can’t go on and be frantic. It was definitely a whirlwind of a night.”

Swing performers, who jump in in cases of illness, vacation or injury, don’t slide into big roles like Alexander Hamilton or Aaron Burr. That’s done by understudies who are typically in the ensemble playing supporting parts (or “tracks”), singing and dancing in the crowd scenes that propel the musical history across decades.

“If Hamilton is out, our ‘Man 5’ will step into the role of Hamilton, and I will be Man 5,” explains Desmond Nunn, 27, a “Hamilton” swing who, one way or another, is on most nights. “Our Man 6 covers Hercules Mulligan and George Washington. Our Mulligan is on vacation this week, so I knew I was doing four shows as Man 6. Sometimes you’re scheduled for four shows, and the rest of the week is kind of a ‘Jeopardy!’ You don’t know who you’re going to be.”

“It took time to mentally and emotionally come to terms with it, and to get used to the job,” says Yvette Lu, a 23-year-old covering all five female ensemble tracks. “But it really is a rewarding position. It keeps me on my toes. Keeps my brain moving.”

If you catch “Hamilton” in the Kennedy Center Opera House, Guzman may be Samuel Seabury, Charles Lee, George Eaker, James Reynolds, the doctor and/or the Schuyler girls’ father — or he may be offstage but ready just in case. For good measure, Guzman understudies the John Laurens/Philip Hamilton role. He’s also one of the show’s dance captains, helping make sure the story-rich dancing stays true to choreographer Andy Blankenbuehler’s intentions.

“It’s more powerful when it’s a little smaller,” says Guzman, who moved to New York from Massachusetts at 17 with his brother to be in “Newsies” on Broadway. “A lot of our notes are, ‘You can do less here.’ ”

“Hamilton” has a “swing-out system” that moves performers in and out of the show regularly to keep them sharp; Guzman says that when he was in another recent Broadway musical, some swings went months without performing. “It’s a tricky thing to cast,” Guzman says. “In auditions, how can you tell if they’re good under pressure, and can maintain six tracks in their heads?”

For Nunn, it helps to have a photographic memory, which he recognized as a principal dancer and ballet master at Alabama’s Huntsville Ballet. “I could look at a video and know what everyone was doing,” he says.

Nunn was a high school athlete with scholarship offers that evaporated when he dislocated both knees in the last basketball game of the season. He went to the University of Alabama on an academic and dance scholarship; ballet had been rehab for an earlier injury, and he loved it. Nunn loved opera, too, and studied voice. But when he moved to New York a few years ago, it was in hopes of getting into “Wicked” or “The Lion King.”

Nunn auditioned for the Broadway revival of “Cats,” and Blankenbuehler passed his information to the “Hamilton” team. He had no New York theater credits and had never been a swing.

“It took a while, especially with this show and all its specifics, to just be able to breathe and enjoy it,” says Nunn, who covers all six male ensemble tracks. He has friends deliberately making careers as swing performers. The jobs aren’t in the limelight’s direct heat, but they are essential to long-running, big-cast shows.

The full-bodied “Hamilton” company last year in San Francisco. (Joan Marcus)

That’s not Nunn’s long-term goal, though he would still love to get into “Wicked” and “The Lion King.”

“Being in an original Broadway cast would be great,” Nunn says. “Taking more responsibility here would be great, too. Add some principal tracks to my swing life.”

Lu is in her very first professional job out of college at New York University’s Tisch School of the Arts, and she didn’t know she was being considered as a swing until she was hired.

“Then I realized my audition process had been a test for that,” she says. Auditions were a week of “boot camp,” full days with performers learning multiple parts and then being asked to switch without warning. Lu groused to another auditioner, “Can you imagine being a swing for this show? That would suuuuck. I would never do that.”

Now she says, “I was so frustrated — ‘They’re not going to see me do stuff! This is so unfair!’ But that’s exactly what a swing does. You just have to jump in.”

With fewer female ensemble members in “Hamilton,” Lu is onstage less than Nunn and Guzman. Naturally, there are nights when it’s tough to watch from the wings. “It’s a little easier on our bodies,” says Lu, who studied dance growing up in St. Louis. “But more frazzling for the brain.”

Lu eventually wants to pursue film and television acting, but she can see herself sticking with “Hamilton” longer, and even taking more swing work.

“It’s such a specific brain to be a swing,” she says. “Growing up dancing, you learn to pick up things fast, and it gets into your muscle memory. When I go back into a track I haven’t done in a while, if I’m overthinking or nervous, I get tense, and that’s when I might mess up. Remembering that I’ve done it before and that it will be okay, and not putting pressure on to be perfect, it all just comes out.”

Like Guzman and Nunn, Lu strictly monitors her fitness and considers each day how much to rest and how much energy to spend on dance or voice classes, or visiting the sights as the company tours the country. “Maintaining myself for the surprises that are going to come,” Lu says, “it’s a whole lifestyle thing.”

If you go

Kennedy Center, 2700 F St. NW. 202-467-4600.

Dates: Through Sept. 1.

Tickets: $199-$725.