Image caption Seal training is gruelling, and many recruits drop out

The men who rescued two hostages from captivity in Somalia were part of the same elite special forces unit that killed Osama Bin Laden. Who are they?

The Bin Laden raid was years in the planning but took just 40 minutes to execute.

More than a dozen members of the US military were dropped near the high-walled, three-storey compound on the outskirts of Abbottabad in north-west Pakistan.

After a brief firefight, five people were killed, including Osama Bin Laden, who reportedly received a shot above his left eye.

All the US forces escaped unharmed, despite technical problems with one helicopter that they had to leave behind.

It says everything about their presence of mind that despite the dangers, they collected hard drives, DVDs and documents from the building before they left.

From the US point of view, the mission, codenamed Geronimo, could hardly have gone any better, a reflection on the preparation and skills of the men who carried it out.

I never thought about dropping out Stew Smith, former Seal on the gruelling training

Although there has been no official confirmation which team was involved, it is widely understood that it was the Seal Team Six (ST6), officially known as the Naval Special Warfare Development Group, but more commonly known as DevGru.

Now, eight months later, the Pentagon has confirmed members of the same team have parachuted into Somalia and freed a Danish man and an American woman kidnapped by reported criminals in October.

The hostages were unhurt, and nine of their captors are said to have been killed. No casualties have been reported among US forces.

The troops were the all-star, elite group of Seals, a team of military personnel trained to carry out top secret operations.

The Seals are part of the Navy Special Warfare Command, and are also the maritime component of the US Special Operations Command, continually deployed throughout the world in operations to protect US interests.

Seal Team Six (ST6) Elite force of Seals, based near Virginia Beach

Selected from all the units, to carry out the most demanding missions

Usually have five years of experience already

The unit belongs to the Joint Special Operations Command (JSOC) which is run at a cost of more than $1bn a year

Involved in Yemen, Somalia and Afghanistan in recent years

Existence shrouded in mystery

They reportedly train around the clock and can spend 300 days a year away from home

There are 2,500 Seals in total, and they take their name from the environments in which they are trained to work - sea, air and land. But it is their highly specialised training to operate in water that they are best known for.

Their missions can be enormously varied in nature, involving combat, anti-terrorism and hostage rescues.

These guys are America's thoroughbreds, says Don Shipley, from Virginia, who spent two decades in the Navy as a Seal.

"They're the finest guys America has. Your average guy walking down the street just doesn't have it.

"The guys that become Seals have gifted eyesight, above average intelligence, and are genetically built to withstand a lot of punishment, being pounded a lot. Those are the guys that are qualified to get in but the guys that ultimately come out are thoroughbreds, they're racehorses."

Image caption New Seals train for an additional year before they are deployed

It is often described as the toughest training available to any special forces anywhere in the world. The drop-out rate is 80-85%.

Stew Smith, a Seal for eight years, now runs fitness training courses in Maryland for people who are thinking of joining up.

He says the first six months of Seal training, known as Basic Underwater Demolition (Buds) is the toughest. It includes one period which lasts a continuous 120 hours, and involves swimming, running, obstacle courses, scuba diving and navigation.

A Buds training course last year lost 190 recruits out of 245 after only three weeks, he says.

"I never thought about dropping out. People ask me why not, and I say that you have to go there in a mindset of competing, not just surviving.

"If you're running your first marathon, your goal is just to finish the thing, you're in a survival mode. But when you're stretching out before, you look across and see a Kenyan who is trying to drop a minute off his best time.

"There is a different mindset. For me, every day in training was a competition."

After Buds, you are officially a Seal and assigned to a team but you need to have another 12 months of training with your new colleagues before you are deployed, says Mr Smith.

Image caption Navy Seals have seen plenty of action in Afghanistan

He believes what makes Seals special is their versatility.

"Also, having a strong confidence with the boat, and a relationship with the Navy, we have a way of respecting Mother Nature because we realise that when you're out there in the middle of the ocean, you're just a speck."

This familiarity with the vagaries of the weather teaches Seals to always have a Plan B, he says. "There's a saying in the Seals that two is one and one is nothing."

The origins of the Seals can be traced to World War II, and its predecessors like the Naval Combat Demolition Unit, which was involved in the invasion of North Africa in 1942.

Their formation came out of a $100m (£61m) package by President John F Kennedy to strengthen the US special forces capability.

They were later involved in Vietnam, Grenada and in Panama, where four Seals were killed as they tried to prevent leader Manuel Noriega escaping by destroying his jet and boat.

The episode was also renowned for an incident a few days later, in which loud rock music was played all day and night to force him out of his refuge in Panama City.

In more recent years, the Seals have been heavily involved in missions in Afghanistan and Iraq.

But their roles in the death of Osama Bin Laden and the hostage rescue adds two more chapters in their history.