Seven people have been detained after special forces personnel boarded an oil tanker off the Isle of Wight after reports its crew had been threatened by stowaways.
Hampshire police had requested military assistance in dealing with the situation on board the 228-metre Nave Andromeda.
The Ministry of Defence announced on Twitter on Sunday night: "In response to a police request, the Defence Secretary and Home Secretary authorised Armed Forces personnel to board a ship in the English Channel to safeguard life and secure a ship that was subject to suspected hijacking.
"Armed forces have gained control of the ship and seven individuals have been detained.
"Police investigations will now continue. Initial reports confirm the crew are safe and well."
It is believed the Royal Navy's crack Special Boat Service troops were used in the mission.
The SBS, a naval special forces unit that works closely with the Special Air Service (SAS), is based in Poole in southern England.
Defence Secretary Ben Wallace said: "I commend the hard work of the armed forces and police to protect lives and secure the ship.
"In dark skies, and worsening weather, we should all be grateful for our brave personnel. People are safe tonight thanks to their efforts."
Speaking shortly before the military action was confirmed by the MoD, Bob Sanguinetti, chief executive of the UK Chamber of Shipping, said: "We understand the vessel has been boarded by security forces and made safe.
"We commend the swift action taken by UK personnel to secure the vessel and most importantly the safety crew."
Concerns were raised with police over the welfare of the ship's crew, shortly after 10am on Sunday, Hampshire Police earlier said.
Police said the vessel, located around six miles off the coast of Bembridge on the Isle of Wight, had been travelling in the direction of Southampton.
It added in an earlier statement on Sunday evening: "It was reported that a number of stowaways were on board, and they had made verbal threats towards the crew. No one has been reported injured.
"An exclusion zone, with a three mile radius, is currently in place near the vessel."
Police were said to be working alongside the Maritime & Coastguard Agency and Border Force in responding to the incident.
John Thompson, co-founder of Ambrey, a maritime security firm advising the ship's Greek owners on Sunday, told the Financial Times that the incident was "definitely not a hijacking".
"It's stowaways who have got a bit rowdy with the crew," he told the newspaper.
According to maritime tracking websites, the Nave Andromeda had sailed from Lagos, Nigeria, on October 5.
It is understood the tanker had been expected to dock in Southampton at 10.30am on Sunday and that the port received contact from the ship but it had not been refused entry to the harbour.
Two coastguard helicopters were scrambled to the scene and spotted circling the ship on Sunday afternoon.
Richard Meade, managing editor of shipping news journal Lloyd's List, earlier wrote on its website that he had received information that there were seven stowaways on board.
He said it was understood that the stowaways had been onboard since the ship left Nigeria, although it had also made anchorage stops in Las Palmas in the Canary Islands and south of Sant Nazaire, France.
Meade said: "The information I have got is that it was a case of stowaways being discovered on board and when the crew tried to get them into a cabin and tried to get their information, there was no documentation."
He alleged: "They tried to get them into a cabin and that's when the stowaways got violent - that doesn't strike me as a hijacking, it's a matter of stowaways."
The latest incident comes after similar situation in December 2018 when British forces stormed an Italian cargo ship and regained control after stowaways threatened crew as it sailed close to the southeast coast of England.