A storm on Sunday complicated the search for an Argentine navy submarine missing in the South Atlantic with 44 crew members, as authorities tried to verify that recent satellite calls seen as a sign the sailors were alive came from the vessel.
U.S. airplanes carrying subsurface search specialists arrived in Argentina to help hunt for the ARA San Juan, which was 432 km off Argentina's coast when its location was last known early on Wednesday, said navy Admiral Gabriel Gonzalez.
More than a dozen boats and aircraft from Argentina, the United States, Britain, Chile and Brazil had joined the effort.
Authorities have mainly been scanning the sea from above as waves of up to 8 meters (26 feet) and winds of up to 40 knots made the search difficult for boats, Gonzalez told reporters.
"Unfortunately these conditions are expected to remain for the next 48 hours," Gonzalez said from the Mar del Plata naval base, about 420 km (240 miles) south of Buenos Aires where the submarine had been heading toward before vanishing.
The defense ministry has said the submarine appeared to have tried to make contact through seven failed satellite calls on Saturday between late morning and early afternoon. On Sunday afternoon, Gonzalez said it was still not clear whether the calls were sent by or to the vessel.
"What we are trying to do today is geolocate those calls to see if they correlate with any point in the operation zone that would suggest it is the San Juan submarine," navy spokesman Enrique Balbi told reporters on Sunday afternoon.
The government was working with Iridium Communications Inc to trace the location of the calls.
A search of 80 percent of the area initially targeted for the operation turned up no sign of the submarine on the ocean's surface, but the crew should have ample supplies of food and oxygen, Balbi said.
The navy said an electrical outage on the diesel-electric-propelled vessel might have downed its communications. Protocol calls for submarines to surface if communication is lost.
Three boats left Mar del Plata on Saturday with radar detection probes and were following the path that the submarine would have taken to arrive at the base in reverse, Balbi said.
"Those probes allow the boats to sweep the ocean floor during their journey and try to make a record of the floor in three dimensions," Balbi said.
The U.S. Navy said its four aircraft were carrying a submarine rescue chamber designed during World War II that can reach a bottomed submarine at depths of 850 feet and rescue up to six people at a time. The chamber can seal over the submarine's hatch to allow sailors to move between the vessels.