Buenos Aires — A multinational armada of aircraft and vessels battled high winds and giant waves Sunday as they scoured a patch of the south Atlantic for signs of a missing Argentine submarine.

There has been no contact with the ARA San Juan, a German-built diesel-electric submarine with 44 crewmembers aboard, since early 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 revived when the navy said Saturday that naval bases had received seven satellite calls attributed to the submersible.

The signals were received at 10:52 a.m. (1352 GMT) and 3:42 p.m .(1842 GMT) on various naval bases with the help from US satellite communication experts, but they did not lock in, thus preventing a full connection.

“Right now, we are working to pinpoint the exact location of what is emitting the signals,” presuming that it could be the missing sub, Argentina’s defense ministry said.

The calls revived hopes that the submarine has surfaced, but a powerful storm that has whipped up waves reaching seven-meters (23 feet) high has made geolocation difficult, officials said.

There is a feeling of “cautious enthusiasm,” naval expert Fernando Morales told C5N television on Sunday.

He said the attempt to use a satellite phone indicates that “the submarine had to emerge to a depth that allowed the call.”

The last regular communication with the San Juan was at 1030 GMT on Wednesday, when the submarine was 430 km off the coast in the Gulf of San Jorge.

Rescuers are focusing on an ocean patch about 300 kilometers in diameter located about 430 kilometers from the coast of the southern province of Chubut.

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 crafts designed to rescue trapped submarine sailors at different depths, as well as a remotely operated underwater robot known as an ROV.

“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.

“That gives us hope, because we knew that if they were down below, they would be screwed,” he told TN news from the western city of Mendoza.

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.

The San Juan is a TR-1700 class submarine which 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 kilometers south of Buenos Aires.

Among those on board is Argentina’s first female submarine officer, 35-year-old weapons officer Eliana Krawczyk.

It is one of three submarines in the Argentine fleet.

Sixty-five meters (213 feet) long and seven meters (23 feet) wide, it was built by Germany’s Thyssen Nordseewerke and launched in 1983. — AFP