World News

Argentina's missing submarine: What we know

Posted November 19, 2017 9:04 p.m. EST

Efforts to locate an Argentine submarine that has been missing since last week have been ramped up dramatically by a multinational search team of boats and planes, the country's navy says.

"We have tripled the search effort, both on the surface and underwater, with 10 airplanes," said Gabriel Galeazzi, a spokesman from the Mar Del Plata Argentine naval base.

Ships and aircraft from at least seven countries are scouring the southern Atlantic for the submarine ARA San Juan, which was last seen Wednesday.

"We have 11 ships from the Argentine navy, from municipalities, and from countries that have collaborated with research ships such as Uruguay, Chile, Brazil, Peru, the United States, and (the U.K.).

"These ships are following the submarine's planned route, (and are) sweeping the whole area and we also have navy ships sweeping from north to south and from south to north."

Here's what we know -- and don't know -- about the disappearance of the ARA San Juan:

When was it last heard from?

The San Juan was last spotted Wednesday in the San Jorge Gulf, a few hundred kilometers off the coast of southern Argentina's Patagonia region and nearly midway between the bases.

On Friday, the navy said they were "conducting operations to resume communications with the ARA 'San Juan' submarine," according to a tweet.

The submarine may have tried unsuccessfully to contact naval bases seven times on Saturday. Argentina's defense ministry said calls came to different bases between 10:52 a.m. and 3:42 p.m. Saturday, and lasted between four and 36 seconds.

Signals received from the area were being analyzed, but are still not determined to be from the crew. If they were sent from the San Juan, they could have originated from a satellite communication device, or from an emergency beacon which could be deployed by the vessel.

"We do know they have an emergency satellite communication system," William Craig Reed, a former US Navy diver and submariner, told CNN. 

"That is a buoy that will pop up to the top. They can send signals from this. They believe that might be the case. Although, unfortunately, it's not panned out. They have not been able to triangulate the signals. There's no way to confirm that they came from the submarine."

What could have happened?

The vessel could have suffered some sort of "catastrophic failure," Reed says.

But, he adds, it "could be something minor that has caused them to either be hung up somewhere or they are on the bottom."

As the San Juan is a diesel submarine, not a nuclear-powered one, "it has a limited life underwater," Reed says.

Time is ticking for the 44 submariners on board.

While submarines of this size and class can stay at sea for around a month, "that doesn't mean they have 30 days underwater. "It's dependent upon the last time they actually recharged their batteries, how long ago they refreshed the air, what's inside the submarine. We just don't know."

If it has sunk but is still intact, they will have about a week to 10 days of oxygen, Peter Layton, a Visiting Fellow at the Griffith Asia Institute, Griffith University says.

How often would the crew usually be in contact?

From a crew comfort point of view the sub would very likely travel submerged around 50 meters (165 ft) below the surface, Layton says, only coming near the surface to "snort" -- replenish its oxygen, recharge the batteries by using the diesel engines, and send radio signals -- around once every 24 hours.  

However, it could depend on whether it was a straightforward transit or if the sub was engaging in other operations en route, Euan Graham, Director, International Security, of the Lowy Institute for International Policy in Sydney told CNN.

"Obviously the Falkland Islands are an intelligence target for Argentina. There is no reason to suggest that it was engaged in this but still a possibility. If so it would need to stay out of detection envelope."

How hard is it to find a sunken sub?

Finding a vessel that is designed not to be found is more difficult "by an order of magnitude" than a regular shipwreck, Graham says.

"In general terms they're designed to be stealthy platforms," he says. "They are difficult to detect underwater... by an order of magnitude."

Finding large objects on the seabed is problematic, Layton says.

They are usually found by listening passively, hope to hear the engines, or by active sonar.

"If you're sitting at bottom of ocean, you're probably not making a lot of noise," he says. "You can't recharge oxygen, can't run too much equipment."

Sonar is only really effective when you're looking for a sub "between the sea floor and the surface, but this one is on the ocean floor.

"What you need is something that maps the sea floor," similar to the devices used in the MH370 search, he says.

What sort of shape is the sub in?

The San Juan is an old diesel submarine, built in the mid-1980s, but was refitted with new engines and batteries around five years ago, Graham says.

"The hull dates back to '85," he says."But it shouldn't lose electric power catastrophically."

Because of the expansion and contraction of the hull as it ascends and descends deep below the ocean's surface, they are designed to have a shelf life of usually around 30 years. That shelf life has expired, Layton says.

Assuming the hull is still intact, it can withstand ocean depths up to around 5-600 meters. If it's resting on Argentina's continental shelf it is likely in waters shallower than this, but if it sank in the depths of the Atlantic Ocean it likely sank below its "crush depth" -- the depth at which the hull buckles under pressure.

Is anything hampering search efforts?

Southern Argentina's Patagonia coast is notorious for strong storms.

"Currently a powerful low-pressure system is causing wind gusts in excess of 70 kph (around 45 mph) and churning up the South Atlantic Ocean with swells equivalent to a two-story building. This weather will hamper the search efforts for at least the next 48 hours," CNN Meteorologist Derek Van Dam said.

Given the submarines range, the search area could comprise "thousands of square kilometers," says Layton.

"If satellite signals are from sub this whittles things down, gives (search and rescue) a great chance."

Can't they send another submarine to find it?

"What is needed is what is in the area, above all, boats with multi-beam sonar, to be able to do the search properly," Argentine naval captain Hector Alonso said.

"Sending a submarine to the area to perform some type of search wouldn't add anything because they don't have the technology or the elements to be able to do an underwater search."

However, at least one specialist rescue sub will be required if the San Juan is found with the crew still alive. Given that it was constructed in Germany, the design is NATO-compatible, and the US is sending a rescue submersible to the area to undertake a rescue.

Assuming it's found, how will the crew members be rescued?

Even if it can be located it will take more time to get a rescue vessel there, the transit time for which could add another couple of days, Graham says, which is problematic when oxygen supplies are diminishing, especially when surface conditions are so rough.

"It's difficult to operate in 8 m (26 ft) waves," he says. Adding to the difficulties of a rescue, we currently "don't know what depth it is located, (and) how precarious the state of the hull could be."

The condition of the sub, assuming its resting on the continental shelf is also of key concern.

"The sunk submarine needs to be sitting upright -- or nearly so -- on the sea floor so the rescue hatch(es) can be easily reached and docked with," Layton says. "The sea floor, though, is not flat. If the submarine is lying at an acute angle docking could be hard."