“The floor is moving!” warned ballet master Antonio Castilla, as the dancers of the English National Ballet loosened up at the barre. The warm-up apparatus had been set up on the stage of the Royal Court Theatre, the plush, 1,000-seat theater on the Queen Mary 2, the flagship of the Cunard line, on the second day of an eight-day crossing in August from Southampton, England, to New York.

The dancers on this unusual summer voyage — high art on the high seas — were accustomed to the laws of aerodynamics. But here in the middle of the Atlantic Ocean, hydrodynamics were their newfound adversary. You could feel the massive ocean liner, a fifth of a mile long, with a capacity of 2,691 passengers and crew of 1,173, rocking and swaying as it cut through the waves at 20 knots.

Among the things that rocked with it were ballerinas on pointe.

“It’s taking it step by step, not knowing what’s going to — you know — where you’re going to be!” said Francesca Velicu, a Romanian-born junior soloist who was performing sequences onboard from “Le Corsaire” and “Don Quixote.” “Because you know, it’s the waves!”

Or, as Castilla put it: “The first day of rehearsal, it was rough. I remember waking up and hearing the creaking of the wood. It was really scary.”

Choppy sea or no, a seven-night Atlantic crossing on a ship of this scale betokened the luxe adventures of another era: If one could blot out the throngs in T-shirts and sweats at the lunch buffet, one might imagine a scene out of the Gilded Age. The shipboard presence of classical ballet certainly reinforced an illusion of timeless enchantment. Cunard called the program “Dance the Atlantic,” and for those intrigued by the art form, it made the crossing especially enticing.

The week-long sharing of sea air with the London-based ballet company, founded in 1950 by dancers Alicia Markova and Anton Dolin and producer Julian Braunsweg, accorded passengers a unique peek behind the scenes. Three formal performances and 16 workshops, classes, discussions and rehearsals were open to the Queen Mary’s voyagers on this crossing, the company’s second with Cunard (the first was before the pandemic, in 2019). For travelers curious about ballet preparation and training, about how a pas de deux is created, about communication between partners, and the vital role of the ballet master, it was like enrolling in a floating dance academy.

For those not intimately acquainted with ballet, the experience could be an invitation to a new passion. “We had a lady in the elevator who said that she was crying, she had not actually watched ballet before,” said Daniel McCormick, a California-bred first soloist with the company, and Velicu’s partner onstage.

“It’s really special for us to be able to come here and show people who enjoy the finer things in life our fine art,” he added. “But there are those people who are just stumbling upon it, and because of that, it’s even more special for us, because we get to show it to a new audience.”

McCormick and Velicu, who have been dancing together for about five years, were one of three pairs of dancers in the hour-long anthology production the company performed on the fourth, sixth and seventh days of the trip. Julia Conway and Miguel Angel Maidana danced variations from the 20th-century Russian ballet “Flames of Paris” and the mambo-flavored “Cha Cha and Tiara,” created for the company by Rentaro Nakaaki. Ivana Bueno and Eric Snyder performed selections from “Sleeping Beauty” and “Swan Lake.”

Sitting in the orchestra watching a dress rehearsal one afternoon were Snyder’s mother, Anna Maria, and his older brother, Robert, from Yuma, Ariz., where Eric started dancing, at the Yuma Ballet Academy, at age 9.

Both were happy to confide 22-year-old Eric’s accomplishments, including his having been invited to join the English National Ballet as a teenager, after being spotted in a European ballet competition. “I thought the gods of dance were going to take you away very young,” Anna Maria remembered telling her son. “But not this young!”

The passengers on the Queen Mary themselves ran a gamut of nationalities, and ages: There were a surprising number of young people on board, as well as middle-aged couples and those of more senior vintage. One morning midway through the crossing, all were represented on the dance floor of the Queens Room, as Jenna Lee, who had spent a dozen years as a soloist with the ballet company, led a class in the creation of one of ballet’s best-loved exhibitions of exuberant synchronicity, the “Dance of the Cygnets” from “Swan Lake.”

“Swans, let’s see you on the floor!” Lee said, as 31 women (and one man) broke into flocks of four, linking arms in the signature pattern of the dance. “When we do the arms, we want to feel the back is really resisting,” Lee instructed. “It does something different to the chest, and it feels nice.”

As company dancer Kate Hartley-Stevens patrolled the perimeter, guiding the quartets, company pianist Julia Richter played the famous passage from the Tchaikovsky ballet. And off they went, 12-year-olds in step with 75-year-olds. “In the end, they just want to feel like they’re dancing,” Lee said after the amateur swans had finished their routine with a self-satisfied round of applause.

The professionals had the far more exacting task. In the open rehearsals, a spectator could see their struggles, not so much with the recorded music as with physics. At times, Snyder and other dancers had to stop in the middle of a sequence, grimacing and shaking their heads. Cunard had imported a special sprung floor for the dancers, but the ship’s movement was still throwing them off.

“The body of the dancer is very, very sensitive to the changes,” Castilla explained during a break from rehearsals. “We have such an incredible sensitivity.”

After a few days on the ship, I stopped noticing any movement underfoot at all. The dancers had not. “Right now, it’s not moving as much, but still there’s still a slide,” said Castilla, who trained and danced in his native Spain before moving on to companies in San Francisco and London.

“We work down into the floor and then from the floor we adjust up, and unless you do it from the floor, it’s just fake,” he explained, as if the floor itself were a dancer’s partner.

“So, yeah, I said, ‘Okay, well, this floor is moving. So, the floor is going, and you have to just find how you relate to the floor.’”

And to the person who’s going to lift you overhead. Velicu and McCormick know each other so well that an ease and confidence are built in. Still, extra vigilance becomes part of the learning curve on the ship, too. “You need to be aware of your own body a lot more,” Velicu said.

“I feel like sometimes when we go onstage, we just do everything by muscle memory, especially the technical elements. So you don’t really think much,” she said. “But then when you have this challenge, it’s a lot different. Just being very careful and taking our time not just rushing into the steps and just going wild.”

As often happens with real pros, the dancers made their mental and physical adjustments. Castilla helped with some tweaks to the choreography that anchored the dancers’ bodies a bit more firmly on that floor. The performances were airy, sensual, assured, dynamic, where they were supposed to be — a touch of grace, thousands of miles at sea.