US Navy P-8 Poseidon patrol planes have joined an worldwide search for the Argentine Armada submarine San Juan, and the Navy has prepared submarine rescue vehicles and four uncrewed underwater vehicles (UUVs) to assist in the search as well.
An air and sea search is under way with help from countries including Brazil, Britain, Chile, the United States and Uruguay.
The communication attempts received on Saturday were originally thought to indicate that the crew was trying to re-establish contact, prompting emotional celebrations by family members and officials.
However, the navy was unable to confirm that those calls originated from the submarine.
Navy spokesman Enrique Balbi says Monday that a USA aircraft was sent to check an area where the noise was heard by two Argentine Navy ships.
It comes after it was revealed the submarine had reported a mechanical breakdown in its final communication. "We still have no established contact", Balbi said, as cited by Clarin.
Weather conditions in the region have made the search hard, spokesmen said, with 6-8 meter (20-26 foot) waves prevailing there in recent days.
There is a feeling of "cautious enthusiasm", naval expert Fernando Morales told C5N television.
Seven brief satellite calls over the past few days to Armada Argentina bases may have been made by the submarine's crew.
Waves up to 20-feet in the area where the sub went missing, about 260 miles from the Argentine coast, were complicating the global search effort, Adm. Gabriel Gonzalez, commander of the base, was quoted by The Associated Press as saying.
Rescuers are focusing on an ocean patch about 300 kilometers in diameter, radiating from the last point of contact.
Sailors with the San Diego-based Undersea Research Command are aiding in the search with a submarine rescue chamber and four aircraft, officials said. The Bluefin 12D is capable of conducting search operations at 3 knots (3.5 mph) at a maximum depth of nearly 5,000 feet for 30 hours, while the Iver 580s can operate at a depth of 325 feet, traveling at 2.5 knots (2.8 mph) for up to 14 hours. The craft was navigating normally, underwater, at a speed of five knots toward Mar del Plata when it was last heard from, he said. Such mechanical problems are not uncommon and numerous backup systems are in place should such an incident occur, Galeazzi said.
The sub was heading from a base in southern Argentina's Tierra del Fuego archipelago to Mar del Plata. "Thank God", he said.
The navy has not ruled out any hypothesis.
The vessel was returning to the Mar del Plata Naval Base south of Buenos Aires at the conclusion of a routine patrol to the far southern port of Ushuaia.
It is one of three submarines in the Argentine fleet. Built in Germany by Nordseewerke, it underwent mid-life maintenance in 2008 in Argentina.
Intermittent satellite communications had been detected on Saturday and the Navy had said they were likely to have come from the submarine.
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