MAR DEL PLATA, Argentina – More help was arriving in a multinational search Thursday for a missing Argentine submarine with 44 crew members as concern grew that the vessel's oxygen supply could soon start to run out.
Britain's Ministry of Defense sent a special helicopter with emergency life support pods to join the hunt that includes planes and ships from a dozen nations.
The Argentina navy spokesman, Capt. Enrique Balbi, said Wednesday that searchers were returning to a previously scanned part of the ocean after determining that a previously unnoticed "hydro-acoustic anomaly" was detected Nov. 15, just hours after the final contact with the ARA San Juan.
He said Argentine navy ships as well as a U.S. P-8 Poseidon aircraft and a Brazilian air force plane would return to the area to check out the sound, which originated about 30 miles north of the submarine's last registered position.
U.S. Navy Lt. Lily Hinz later said the unusual sound detected underwater could not be attributed to marine life or naturally occurring noise in the ocean.
"It was not a whale, and it is not a regularly occurring sound," Hinz said.
The San Juan, a German-built diesel-electric sub, went missing as it was sailing from the extreme southern port of Ushuaia to the city of Mar del Plata, about 250 miles (400 kilometers) southeast of Buenos Aires.
Experts worry that oxygen for the crew would last only seven to 10 days if the sub was intact but submerged. Authorities do not know if the sub rose to the surface to replenish its oxygen supply and charge batteries, however.
More than a dozen airplanes and ships are participating in the multinational search despite stormy weather that has caused waves of more than 20 feet (6 meters). Search teams are combing an area of some 185,000 square miles (480,000 square kilometers), which is roughly the size of Spain.
The U.S. government has sent two P-8 Poseidons, a naval research ship, a submarine rescue chamber and sonar-equipped underwater vehicles. U.S. Navy sailors from the San Diego-based Undersea Rescue Command are also helping with the search.
Henao reported from Buenos Aires. AP writer Julie Watson in San Diego and Debora Rey in Buenos Aires and AP video journalist Paul Byrne in Mar del Plata contributed to this report.