There had been no contact with the ARA San Juan since early Wednesday, according to the navy, prompting Buenos Aires to launch an air and sea search with help from countries including Brazil, Britain, Chile and the United States.
The entire search area has been scoured by ships and aircraft, despite storm conditions that complicated the effort, Argentine navy spokesman Enrique Balbi said yesterday.
Yet finally seven satellite-transmitted signals believed to be part of the vessel trying to resume contact were detected, the Defence Ministry said.
"Right now, we are working to pinpoint the exact location of what is emitting the signals," presuming that it could be the missing sub, the ministry said.
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Brazil, Britain, Chile, the United States and Uruguay took part in the aerial side of the search, and Washington said it was sending rescue help.
The California-based Undersea Rescue Command was deploying two independent rescue assets -- including a pressurised rescue module -- to help in the hunt for the missing sub.
All land communications bases along the coast were ordered to be scanning for any followup, as family members of the missing waited nervously in Mar del Plata.
Claudio Rodriguez, whose brother Hernan is aboard, was hopeful and thought the vessel would be found afloat, if the satellite signals were able to be sent.
"They've got to be afloat. Thanks God," Rodriguez stressed.
"That gives us hope, because we knew that if they were down below, they would be screwed" he told TN news from Mendoza.
TR-1700 class diesel electric submarine had been returning from a routine mission to Ushuaia near the southernmost tip of South America, to its base at Mar del Plata, around 400 km south of Buenos Aires.
Among those on board is Argentina's first female submarine officer, 35-year-old weapons officer Eliana Krawczyk.
The San Juan is one of three submarines in the Argentine fleet.
Sixty-five metres (213 feet) long and seven metres (23 feet) wide, it was built by Germany's Thyssen Nordseewerke and launched in 1983.
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