A sea drone was used to save two crew members of a downed US army helicopter off the coast of Oman earlier this week, according to the US military - making it the first publicly known instance of an unmanned vessel being used to conduct a rescue mission.

President Donald Trump said the apache helicopter was shot down by Iran near the Strait of Hormuz - the dangerous waterway which has been largely blocked off to shipping since the start of the Iran war.

The two soldiers "were safely rescued within approximately two hours and are in stable condition", US Central Command (Centcom) said.

BBC Verify has examined what we know about the drone boat and how the mission took place.

What is the US sea drone?

Centcom has confirmed a 'Corsair' sea drone was used in the rescue, which is made by a Texas-based maritime drone manufacturing company.

It's 24 feet (7.3m) long, capable of carrying 1,000lbs (450kg), and can travel more than 35 knots per hour (40mph), according to the company's website.

"The Corsair is about the size of a fishing boat with a flat deck, so it's designed to be loaded and it's probably able to hold three to four people," says Bryan Clark, a naval drone expert at the Hudson Institute policy think-tank.

Clark adds it has a 360-degree camera, a radar system for long range navigation, and an electronic radio sensor to pick up communications for intelligence gathering.

"This Corsair vessel has been around for a few years now - the US Navy has about 50 of them," according to Dr Stacie Pettyjohn, a US military expert at the Center for a New American Security think-tank.

"They're typically used for detecting mines or surveillance, but the Navy is still experimenting with the fleet in the strait to see what it can do."

The sea drone is operated by Task Force 59, the US Navy's first unit dedicated to unmanned systems which was created in 2021, and the US began deploying it in the Middle East in March.

It's part of the Pentagon's plan to expand its use of drones. The Navy awarded the Corsair's manufacturer a $392 million (£293m) production contract for its autonomous vessels last year.

How did the rescue mission play out?

Although the sea drone can be operated autonomously, both experts BBC Verify spoke to said it was probably manually operated for the rescue.

"In this mission it would have likely been controlled remotely by a person with a joystick to make sure they got to the exact location of the crew," Clark said.

"It would have been directed to their known position and they would have just clambered on board, just like would to get on a boat at sea."

The Corsair was used for the mission because of "proximity and capability factors", Centcom spokesman Captain Tim Hawkins said following the rescue.

"The unmanned drone would have been used instead of sending in a ship or a helicopter where people could have been shot at," Dr Pettyjohn says.

"Although rescue isn't a core mission of the vessel, it was clearly good for a dirty, dangerous missions like this."

The US service members were picked up at about 03:30am on Tuesday local time and taken to another location on the water, according to Captain Hawkins. "They were then hoisted up to a helicopter for further transport," he added.

Where are sea drones used elsewhere in the world?

"Most of vessels used by Ukraine are smaller, more like the size of a jet ski, and couldn't carry a person," says Clark.

Yemen's Houthi rebels have also operated so-called kamikaze drone boats, and Iran has used drone boats during this current conflict to target vessels attempting to pass through the Strait of Hormuz.

"The Houthis and Iranians have had sea drones in the past, but Ukrainians really took it to the next level and showed what other countries could do," says Dr Pettyjohn.

"The US sea drones very much emerged off back of the Ukraine war and seeing what they innovated."