LONDON — Under the cover of darkness, British commandos slid down ropes from four Navy helicopters hovering over the English Channel and onto the deck of an oil tanker.
It had been 10 hours since the captain of the ship, the Nave Andromeda, had called for assistance after stowaways onboard threatened violence against the tanker’s crew as it approached shore. Within minutes, the operation off the coast of the Isle of Wight had ended and seven stowaways were in custody.
The Ministry of Defense called the situation on Sunday a “suspected hijacking.” But a representative for the company that manages the vessel said it was not a hijacking and that the captain had remained in control of the tanker.
The BBC reported that members of the Special Boat Service had rappelled down ropes from four Royal Navy helicopters over the vessel on Sunday evening, and that the stowaways were believed to be seeking asylum in Britain.
The Ministry of Defense declined to offer further information on the operation, saying that it was against its policy to comment on special forces operations. The Special Boat Service is an elite counterterrorism unit of the Royal Navy and is headquartered in Poole, a city on the southern coast of England not far from where the ship called for assistance.
The ministry did, however, release a brief statement saying that the armed forces had been given permission to “board a ship in the English Channel to safeguard life and secure a ship that was subject to suspected hijacking.” It said that the forces had gained control of the ship and that seven people had been detained.
Navios Maritime Holdings, the Greek company that owns the Nave Andromeda, said in a statement that the ship’s captain informed the British authorities that stowaways had been found on board, as “he was concerned for the safety of the crew due to the increasingly hostile behavior of the stowaways.”
But a spokesman for the company said that the crew had not lost control of the vessel, even as they took refuge in a secure area of the ship, and that describing the incident as a hijacking was inaccurate.
The trouble aboard the Nave Andromeda — a Liberian flagged vessel — began around 10 a.m. Sunday about six miles off the coast of the Isle of Wight in the English Channel, according to the Hampshire Police, who are responsible for the area.
The tanker had been traveling toward the port of Southampton having left Lagos, Nigeria, three weeks ago. The Hampshire Police are investigating the events to establish the full circumstances.
Ben Wallace, the secretary of defense, in a statement posted to Twitter early Monday, commended the armed forces and the police for their work.
“In dark skies, and worsening weather, we should all be grateful for our brave personnel,” he said. “People are safe tonight thanks to their efforts.”
Tobias Ellwood, a member of Parliament and chairman of the defense select committee, told Talk Radio on Monday that the special forces were involved and that the crew had known about the stowaways for some time before the events played out on Sunday. The threats began as the boat neared shore, he said.
“As soon as word came through that there were seven stowaways on board, and the ship’s crew were not fully in command of the vessel, that would have triggered a multiagency alarm,” Mr. Ellwood said. “And then well-rehearsed protocols, classified protocols, would have been tripped into place covering the full spectrum of potential outcomes.”
Bob Sanguinetti, chief executive of the U.K. Chamber of Shipping, said that stowaways on commercial shipping vessels were not uncommon — on average there were about 90 cases per year with about 230 individuals globally — but that only a small percentage took place in British waters.
“They range from political refugees to economic migrants, people desperate to find a new life somewhere else,” Mr. Sanguinetti said. “And that’s what appears to have been the case in this particular instance.”
Hijacking, on the other hand, is very unusual in shipping, Mr. Sanguinetti said, citing industry protocols aimed at stopping intruders from boarding vessels.
“Clearly you can’t eliminate the risk altogether, and there are instances — as we’ve seen in this case — where people do manage to come onboard,” he said. “That’s when other guidelines kick in.”
When stowaways are discovered, the captain is obliged to report them to the authorities, as the captain did in this case, but also ensure that they are treated humanely and are well cared for while on the vessel.
But if the crew feels threatened, the captain would follow a procedure that involved locking the crew in a “citadel” — a secure location where they could maintain some control over the movements of the ship and communicate with the authorities.
The events on the Nave Andromeda came amid a broader debate about migration and asylum seekers in Britain. Priti Patel, the home secretary, has vowed to overhaul what she calls a “broken” asylum system after illegal crossings of the English Channel increased in the late summer.
Advocates for refugee rights said that although the motivations of the stowaways remained unclear, the events on Sunday pointed to the need for more legal avenues for asylum seekers.
“Many refugees take dangerous risks to find sanctuary in the U.K. because there is a lack of safe and legal routes to get here,” said Mariam Kemple Hardy, head of campaigns at Refugee Action.
Some resort to criminal smugglers to arrive in the country, and the government has yet to restart a refugee resettlement program that has been paused since March, she added.
Mr. Sanguinetti said the British government had sent a clear message “that ships and seafarers will not be allowed to get caught up in the crisis of asylum seekers or economic migrants, as desperate or as sad as they might be.”
“That’s a separate humanitarian issue for governments to look into and address, and allow ships to continue trading around the world,” he said.