Two Navy SEALs went missing at sea during a raid to interdict smuggled Iranian weapons last week.
Western forces have carried out numerous visit, board, search, and seizure (VBSS) missions in recent years.
These operations can be "dangerous" and "complex," a former US Special Forces soldier said.
The two Navy SEALs who went missing during a nighttime operation off the coast of Somalia last week were involved in intercepting a boat that was attempting to smuggle Iranian weapons to the Houthis, the US military said on Tuesday.
Operations like this — interdicting a suspicious vessel — are known as visit, board, search, and seizure, or VBSS. A former US Special Forces soldier said these missions are particularly "dangerous" and "complex" for a number of reasons, including the difficulty of successfully mounting a moving target and the potential to encounter hostiles once on board.
And "when you throw in nighttime, everything gets more complicated," Lino Miani, a retired Green Beret and combat diver, told Business Insider.
Navy SEALs from the USS Lewis B. Puller expeditionary sea base conducted the "complex boarding" of a dhow on Thursday that was illegally transporting weapons from Iran to the Yemen-based Houthis, US Central Command, or CENTCOM, said in a Tuesday statement.
The raid on the small boat occurred in international waters in the Arabian Sea and was supported by helicopters and drones, CENTCOM said, confirming the two SEALs who were initially said last week to be missing at sea were "directly involved" in this operation.
One of the missing SEALs is said to have slipped from a ladder and fell into the water while boarding the boat amid rough seas, leading a second service member to jump in the water and attempt a rescue.
"We are conducting an exhaustive search for our missing teammates," Gen. Michael Kurilla, the CENTCOM commander, said on Tuesday. But the chance of survival after multiple days lost at sea is slim.
Western militaries have carried out numerous interdictions of vessels attempting to smuggle weapons from Iran to Yemen in recent years, and while the US Navy SEALs frequently conduct US military VBSS operations, other elite forces — including US Army Green Berets — also have experience in this area.
These types of missions are not easy tasks, Miani, the president of the Combat Diver Foundation, said, explaining that boarding a boat from the water is difficult to begin with because soldiers have to factor in the sea state, like potentially rough waves, and the speed at which their target is traveling.
Once troops reach the boat, there is the physical process of trying to board it with some sort of device like a ladder or grappling device. This becomes more challenging at night, when there's often a greater incentive to be stealthy. Service members are sometimes working quietly with minimal light, so it can be hard to actually find good attachment points to climb aboard the target boat.
The situation can become even more tricky if the boarding party encounters any hostile crew members aboard. Planning for this scenario involves making sure involved personnel are prepared for an assault with the necessary weapons and ammunition. Gear can be heavy and bulky, making it hard to climb onto the boat and also increasing the risk of drowning if anyone falls into the water.
Miani said that "an opposed boarding operation is probably the most difficult and dangerous mission that a special operations force could engage in."
"It requires the best training and equipment," he said. "It's very complex, both physically and operationally. Commanders are not going to make that decision lightly."
Not all VBSS raids are equally complicated or dangerous, but there's always risks. Details of what exactly the SEALs encountered during their operation are limited. CENTCOM said in the aftermath that the dhow was sunk and arrangements for the 14-member crew are still being determined.
Boarding boats from the water's surface is also not the only method of conducting a VBSS mission. Troops can also descend from helicopters — a technique known as fast-roping.
It's unclear if the helicopters that participated in last week's operation were involved in such an action. But Miani said if this was the case, it could mean that multiple teams boarded the boat through various entry points, a potentially more complex operation that requires significant coordination.
"It's extremely dangerous because [boats] move up and down with the sea state," said Miani, who has personal experience fast-roping onto a ship. "You're trying to get a helicopter to stay over a relatively small target that's moving and could be maneuvering too."
For now, the search for the two missing — and unidentified — SEALs remains ongoing, according to the Pentagon. But time is likely running out.
CENTCOM said it seized Iranian-made ballistic and cruise missile parts — including warheads, guidance, and propulsion — in the operation last week, marking the first time the US Navy has intercepted components like these in over three years. The military said the Houthis have used this same weaponry to attack key international shipping lanes off the coast of Yemen, something the Iran-backed rebels have done relentlessly for months.
"It is clear that Iran continues shipment of advanced lethal aid to the Houthis," Kurilla said. "This is yet another example of how Iran actively sows instability throughout the region in direct violation of UN Security Resolution 2216 and international law," he added, referring to an arms embargo on the rebel group.
"We will continue to work with regional and international partners to expose and interdict these efforts, and ultimately to reestablish freedom of navigation," he added.
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