A multinational armada of aircraft and vessels battled high winds and big seas Sunday as they intensified their search for a missing Argentine submarine after apparent attempted distress calls raised hopes the 44 crew members may still be alive.
There has been no contact with the ARA San Juan, a German-built diesel-electric sub since early on Wednesday.
An air and sea search is underway with help from countries including Brazil, Britain, Chile, Uruguay and the United States.
Hopes of finding survivors were temporarily revived when the navy said Saturday its bases had received seven satellite calls attributed to the submersible.
The signals were received at 10:52am and 3:42pm local time but they did not lock in, thus preventing a full connection.
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Argentine submarine goes missing
But the navy was unable to confirm that those calls originated from the submarine.
The seven satellite calls have not helped to determine the vessel's location, a navy official said on Sunday.
"We analysed these signals, which as we know were intermittent and weak," Gabriel Galeazzi, a naval commander, said.
"They could not help determine a point on the map to help the search."
Seven-metre waves
The calls revived hopes the submarine had surfaced, but a powerful storm whipped up waves reaching seven metres in height has made geolocation difficult, officials said.
Argentine navy spokesman Enrique Balbi said weather conditions were not expected to improve before Tuesday.
Despite the bad weather, "10 aircraft, both domestic and foreign, are in a search rotation 24 hours a day, each in a different area," he said.
There is a feeling of "cautious enthusiasm", naval expert Fernando Morales told C5N television.
He said the attempt to use a satellite phone indicates "the submarine had to emerge to a depth that allowed the call".
The last regular communication with the San Juan was early on Wednesday when the submarine was 430 kilometres off Argentina's coast in the Gulf of San Jorge.
Rescuers are focusing on an ocean patch about 300 kilometres in diameter, radiating from the last point of contact.
The US Southern Command said Sunday that it was sending a second Navy P-8A Poseidon aircraft to join the search. The Florida-based plane and a crew of 21 are to reach Argentina later in the day.
A NASA P-3 research aircraft is already participating in the search, the Southern Command said.
The California-based Undersea Rescue Command also said it was deploying two underwater craft designed to rescue trapped submarine sailors at different depths, as well as a remotely operated underwater robot known as an ROV.
Britain's Royal Navy said it had sent an Antarctic patrol ship "HMS Protector" to join the search.
Mr Balbi said it was following the northwards course the submarine would have taken towards Mar del Plata.
Relatives of crew members unfurled a flag at the naval base that read: "Be strong Argentina, We trust in God, We wait for you."
'Got to be afloat'
"We will do what is necessary to find the submarine as soon as possible," Argentine President Mauricio Macri wrote on Twitter.
All land communications bases along the coast were ordered to scan for any follow-up signals, as family members of the missing waited nervously in the coastal city of Mar del Plata.
Claudio Rodriguez, whose brother Hernan is aboard the submarine, was hopeful, saying the satellite signals suggested the vessel was still afloat and would be found.
"They've got to be afloat. Thank God," he said.
Among those on board is Argentina's first female submarine officer, 35-year-old weapons officer Eliana Krawczyk.
The navy has not ruled out any hypothesis, a spokesman said.
The most likely scenario given is that an electrical problem may have unexpectedly cut off the vessel's communications.
Prayers from the pope
The TR-1700 class submarine had been returning from a routine mission to Ushuaia, near the southernmost tip of South America, to its base at Mar del Plata, about 400 kilometres south of Buenos Aires.
It is one of three submarines in the Argentine fleet.
Sixty-five meters long and seven meters wide, it was built by Germany's Thyssen Nordseewerke and launched in 1983.
It underwent a refit between 2007 and 2014 to extend its use by about 30 years.
At the Vatican, Argentine-born Pope Francis said he offered "his fervent prayer" for the safety of the submarine sailors.
