Not long ago, the Seattle Seahawks looked like a budding dynasty. With the franchise trying to rebuild on the fly, a trip to London came at the worst possible time. Or was it the best?

The N.F.L. told the Seattle Seahawks last winter that they would face the Raiders in London on Oct. 14.

Back then, months before the rest of the 2018 schedule came out, the Seahawks could never have anticipated that last weekend’s trip to London would come at a pivotal juncture for the franchise: Their record stood at 2-3 after a tough loss to the Los Angeles Rams.

Then it was time to spread the gospel of American football overseas. Instead of heading about 670 miles south to Oakland, Calif., the Seahawks would fly nearly 5,000 miles to England, eight time zones away.

Sending an N.F.L. team overseas is a herculean venture. Players need passports, the equipment staff sends supplies months in advance, the travel director has to navigate an unfamiliar airport and hotel, and the trainers will often modify the players’ diet and sleep regimens. Then there is the equipment, some 21,000 pounds of it, that must be transported.

The Seahawks were doing all this while searching for their footing. The cornerstones of the team’s dominant Super Bowl defenses were mostly gone. Russell Wilson, the franchise quarterback, had one year remaining on his contract and was expected to seek a far larger deal. In Week 4, safety Earl Thomas broke his leg and appeared to point his middle finger at the Seahawks’ bench as he was carted off the field. The team owner Paul G. Allen’s non-Hodgkin’s lymphoma, which was in remission, had returned — something that proved far more serious than all but a few realized. (Allen died on Monday.)

Maybe, with pressure mounting, a venture far away was exactly what this franchise needed.

Team equipment personnel prepare shoulder pads and jerseys in preparation for the team’s trip.

Passports for each player were set up on a table with each corresponding boarding pass before the team left for the airport. Players boarded the bus to the airport at the team’s training facility in Renton.

Wednesday, Oct. 10 Flying to London to See an Old Friend

The Seahawks, who had a home game the Sunday before they left for London, practiced the next Tuesday and Wednesday, then left for London on Wednesday night, accompanied by a New York Times reporter and photographer.

In the locker room, the mood was loose. Cornerback Neiko Thorpe challenged all comers in table tennis. At his locker, he had a Nintendo Switch gaming console that he was taking on the trip.

Linebacker Bobby Wagner and other remaining members of the 2013 team, which won the Super Bowl, spoke about facing an old teammate, the enigmatic Marshawn Lynch, now with the Raiders.

“He was who he was, and I think that speaks more volumes about the fun or the type of person that he was that he brought to this locker room more so than anything,” receiver Doug Baldwin said.

Their warm comments were a reminder of how difficult it is to keep winning teams together in the N.F.L. The Seahawks were poised to win their second consecutive Super Bowl when, with the ball near the goal line, they opted to pass instead of hand off the ball to Lynch. The interception and loss that followed, against the New England Patriots, halted any talk of a dynasty and left some players, including Lynch, bitter.

Now they had to defeat Lynch.

They boarded a chartered Airbus A340-600 that included 45 sleeping pods in first class for the veteran players. Coach Pete Carroll sat in the first row of business class along with other coaches. Rookies and members of the practice squad sat behind them. About half the 170 passengers sat in coach, which was filled with giddy chatter before takeoff. The menu was the same for everyone: beef filet, Cajun chicken or herb roasted salmon.

Players grabbed peanut butter and jelly sandwiches on the flight. Veteran players slept in the first class cabin. Brett Carlsen for The New York Times

The Seahawks are fanatical about players’ health, including the science of sleep. For years, players have worn sleep monitors to give trainers a window into how players rest and recuperate. On flights east, Sam Ramsden, the team’s director of health and player performance, tells players to stay awake so they will be tired and sleep well when they arrive.

For this trip, Ramsden reversed the program: He told players to sleep as much as possible on the flight so when they arrived in London on Thursday afternoon, they would have enough energy to stay up until 9 or 10 p.m. and then get a full night’s rest.

“We try to protect their circadian rhythms as much as possible,” Ramsden said.

Ramsden’s staff prepared sleep kits for “mental alertness.” They included blackout eye masks. Some players took melatonin or Ambien, while others used earbuds that played the sounds of wind and rushing water to induce sleep.

A few people slept on the floor or were splayed across a row of seats. Wagner watched game video on his iPad. A half-dozen others, including the twins Shaquill and Shaquem Griffin, played the card game Spades in the bar area in first class. They trash-talked, laughed and threw $20 bills to the winners. They seemed unaware that Carroll, who tries to give his players room to be themselves, was sleeping in a seat a few feet away.

The urgency of the moment seemed intangible — and maybe that was the point.

The Seahawks practiced on the grounds of their hotel in Watford.

Seahawks Coach Pete Carroll spoke to the media in a potter’s shed at the team hotel. Football equipment piled up outside the team’s temporary locker room.

Thursday, Oct. 11 Landing, Then Letting Off Some Steam

The players and coaches rolled off the plane on Thursday about 1:30 p.m. Some players struggled to stay awake, like defensive end Frank Clark, who draped his thick coat over his head.

Buses took them to the Grove, a resort in Watford, north of London, that features grass tennis courts and a golf course.

It has plenty of amenities, but nothing was left to chance. The team shipped 1,150 rolls of athletic tape, two tons of medical supplies, 350 power adapters, 500 pairs of shoes and 240 pairs of socks. In all, the Seahawks had shipped 21,000 pounds of gear and products worth $770,000. Some items — toiletries, snacks, bottled water, Gorilla Glue, lighters (to burn off loose threads) and cayenne pepper, which when mixed with talcum powder keeps players’ feet warm — were ordered from the Amazon U.K. website.

On the way to Top Golf. Doug Baldwin, left, joked around with Jaron Brown while hitting golf balls.

In the evening, the players let off some steam at a Topgolf facility. Broken into groups of four, they tried to hit balls into giant holes to score points, and took grief every time they were wildly off target.

“Is that the best you can do?” Wagner yelled at Austin Calitro, another linebacker.

Thorpe, a cornerback, dug into a pile of chicken wings and posted videos on social media. “This is how I imagined it,” he said of the team’s first day in England.

Wilson was in the first booth and seemed to be taking his swings seriously as the three veteran offensive linemen who sat with him checked their cellphones.

Then, finally, it was time to return to the hotel, for smoothies, bottles of water and sleep.

Lavon Coleman wandered around London for the first time.

Oct. 12 Getting Lost in London With a Few Pints

After several hours of meetings and a practice, some veterans left on a coach bus for Covent Garden and their only chance to see central London. Another bus took about a dozen younger players, with money in their pockets and no family in tow, to Watford Junction station, where they rode the train into London.

At a loss where to go, a few English rugby players, who watched the Seahawks practice that day, helped them find Nike Town at Oxford Circus.

At the front of the store, mannequins dressed in Seahawks gear stood next to racks of N.F.L. jerseys and shirts. “Man, there’s a lot of Patriots stuff here,” Azeem Victor, a linebacker on the practice squad, said. As he looked for a soccer jersey, two shoppers separately asked him for help, assuming he worked there.

Italian tourists asked to take photographs with the players, which made Rashaad Penny, a rookie running back, feel like a rock star. He soon video-chatted with somebody to describe what had happened.

Penny and the other players were enjoying the chance to get away from the endless meetings and practices, and the expectations of their coaches and veterans. Lavon Coleman, another running back, stood wide-eyed in the street as people streamed past. He asked strangers for directions and food recommendations. He posed for pictures with Raiders fans from Denmark.

“I like that I can be myself,” he said.

A group of players went looking for food, but didn’t seem interested in challenging their taste buds. They ended up at a Shake Shack. Linemen Jordan Roos and Elijah Nkansah went to a pub. Surprised by how warm their pints of Guinness were, they went to another pub and ordered lagers that were chilled to their satisfaction. Several more pints were consumed before, with the clock ticking toward the midnight curfew, they made their way to Euston station. There, they bumped into Brett Hundley, the backup quarterback, and several others. The players filled half a train car and compared notes on their first glimpses of London on a commuter train back to Watford Junction.

Pete Carroll, Shaquem Griffin, Shaquill Griffin, Tyler Lockett and Russell Wilson autographed items before a fan event at the hotel.

Saturday, Oct. 13 Visualization and a Blunt Assessment

Carroll takes his players to the stadium the day before a road game so they can visualize conditions ahead of time. At 1:30 p.m., the Seahawks drove to Wembley, where they saw the locker room, which had been set up with their gear, and the field, the most famous soccer pitch in England. Worried about the slickness of the grass, Erik Kennedy, the equipment manager, had longer screw-in cleats available for the players.

Carroll and the team returned to the Grove around 4 p.m. Wilson, Wagner, Baldwin and a few other players got ready to meet two dozen fans in a session that was broadcast on Facebook Live.

In the green room beforehand, the players signed footballs and helmets. Wilson, mindful of his public image, asked a producer if there was anything to worry about. He was assured that the talk was in front of friendly fans.

At the event, Baldwin did not sugarcoat his description of the team, even in front of his coach.

“Pete wouldn’t want to call it this, but it’s a retooling, a process we’re all going through,” he said. “I think we’re doing a great job of bringing the young guys along, of establishing what our culture is again, re-establishing it so the young guys can buy into it. It’s been a difficult process but I think, moving forward, we’re going to be really good.”

D.J. Fluker played the Madden NFL 19 video game before leaving to play the Raiders.

Dwayne Harris of the Raiders and Neiko Thorpe of the Seahawks after the game. Seahawks quarterback Russell Wilson talked to reporters after the game.

Sunday, Oct. 14 Four Thousand Miles for the Win

N.F.L. players do whatever they can to relax in the early hours on game day.

Some Seahawks packed, others looked at yet more video.

D.J. Fluker, the team’s enormous guard, found solace in the players’ lounge, where he sat alone playing the Madden football video game. Fluker, who filled his roster with current and former stars like Antonio Brown and Ronnie Lott, played a virtual foe. He flicked through offensive formations, which he said were similar to those in N.F.L. playbooks. He liked the distraction.

“It takes away my anxiety,” he said. “If I think about football too much, I’ll get antsy. You can be overprepared.”

He didn’t need to worry. From the opening whistle of the game, the Seahawks seemed to have every advantage. The meticulous planning, the sleep kits, the choreographed downtime and maybe even the pints of Guinness seemed to help steady the players at a fragile moment. Or maybe they were just better.

The defense stifled Lynch, the Raiders running back, while Wilson effortlessly led the Seahawks’ offense up and down the field. Final score: 27-3.

As the Seahawks piled back into their locker room, now 3-3 and brimming with confidence, one player yelled, “Four thousand miles for the dub,” a reference to a W, a win.

Inside the locker room, before the news media were allowed in, the players were screaming and slapping shoulders. Rainn Wilson, an actor on the television comedy “The Office” and a big Seahawks fan, was brought in to address the rowdy players. “That was Seahawks football today,” he yelled as players whooped it up.

Then Carroll, his voice hoarse, thanked the staff that organized the trip, “the whole thing.”

Lavon Coleman collected airline pillows on the flight home.

Monday, Oct. 15 A Big Victory, Followed by a Monumental Loss

At 1:30 a.m., the Seahawks departed Gatwick Airport. Coleman, sitting in economy class, collected piles of pillows and built a bed on the floor in front of an emergency exit.

The flight home was far quieter than the one to London. The staff worked overtime during the four-day trip and many of them were asleep before takeoff. Exhausted after three hours of high-powered football, the players lumbered into their pods.

Nearly 10 hours later, the plane landed in Seattle. Carroll spoke over the plane’s intercom, announcing a day off for everyone who did not need to see the training staff. Cheers erupted.

He called it a “great week,” and then said, “To everybody, thanks a lot, appreciate ya, love ya, bye.”

The bliss lasted roughly 12 hours. In midafternoon, word spread that Allen, the team’s owner and a co-founder of Microsoft, had died.

In football and in life, even the best trips come to an end.