ARA San Juan: Navy warns Argentina's missing submarine could soon run out of oxygen

The search for a missing Argentine submarine and its 44 crew members is entering a “critical” stage amid fears it could soon run out of oxygen.

The ARA San Juan disappeared about 300 miles off Argentina’s southern Atlantic coast last Wednesday after reporting a battery failure.

Britain and four other countries are helping Argentina in the search, while crew members’ relatives have gathered at the vessel’s base in Mar del Plata desperately awaiting news.

If the German-built submarine had sunk or was otherwise unable to rise to the surface, it would be winding down its seven-day oxygen supply, Argentina’s navy said.

"Oxygen is a permanent worry. Every day that passes is more critical," naval commander Gabriel Galeazzi said at an evening news conference in Mar del Plata.

More than a dozen boats and planes from Argentina, the United States, Britain, Chile and Brazil have joined the search. Authorities had been mainly scanning from the sky as storms halted the maritime hunt last weekend.

The weather improved on Tuesday, helping search efforts by sea. Wind speed slowed and waves that rose as high as 8 metres at the weekend diminished.

"The search by patrol ships has become more effective thanks more than anything to less pounding by the waves, which have fallen to three or four metres," said navy spokesman Enrique Balbi.

"We have to make the most of today and tomorrow because on Thursday the weather is expected to get more complicated."

Also on Tuesday, authorities investigated white flares spotted in the South Atlantic overnight. Searchers found an empty floating raft, and noticed the flares from a distance. But the raft's brand suggested it did not belong to the ARA San Juan, which was equipped with only red flares for emergencies and green flares for other situations, the navy said.

Searchers have suffered other disappointments.

Analysis of satellite signals and sounds detected by underwater probes, initially thought to be messages from the crew, has found they did not come from the vessel.

"The sounds could be biological. We have discarded the possibility that it was a clanging of morse code against the hull of the submarine," Balbi said.

Relatives of crew members have been gathered at a naval base in Mar del Plata, where the search is being coordinated.

The ARA San Juan was launched in 1983, the newest of three submarines in the navy's fleet, and underwent maintenance in 2008 in Argentina. Its four diesel engines and its electric propeller engines were replaced, according to specialist publication Jane's Sentinel.