The search operation for the missing Argentine submarine, ARA San Juan, got a boost after a multinational search team of boats and planes joined the country's navy. But, the team has not yet been able to find anything substantial about the vessel.

According to a senior US Navy official, on Monday they picked up what were thought to be noises from the missing submarine. This came after the sonar systems of two ships detected noises which were sounding like tools being hit against the hull of a sub.

However, Argentine navy spokesman Enrique Balbi later confirmed that the noises were not from the missing vessel and added that they were possibly from the ocean or marine life.

What do we know so far about ARA San Juan?

The ARA San Juan submarine has been missing since Wednesday (15 November) with at least 44 crew members on board.

Among them is Argentina's first female submarine officer, 35-year-old weapons officer Eliana Krawczyk.

According to Balbi, the submarine was in the southern Argentine sea about 432km from the Patagonian coast on Wednesday morning when it last communicated.

Seven communication attempts were recorded on Saturday. Although they were initially believed to have originated from the vessel, authorities on Monday said the calls did not come from ARA San Juan.

The navy has not yet ruled out any hypothesis but said that there might have been an electrical problem which may have unexpectedly cut off the vessel's communications.

But according to protocol, the submarines need to come to the surface if communication is lost.

Ships and aircraft from at least seven countries are helping the Argentine navy in search of the submarine. The navy on Sunday (19 November) had intensified an aerial search after adverse weather conditions triggered waves up to 26 feet (8 metres) and made a maritime search difficult.

"We have 11 ships from the Argentine navy, from municipalities, and from countries that have collaborated with research ships such as Uruguay, Chile, Brazil, Peru, the United States, and (the UK).

"These ships are following the submarine's planned route, (and are) sweeping the whole area and we also have navy ships sweeping from north to south and from south to north," Galeazzi said.

How long can the crew survive underwater?

According to Balbi, the vessel usually has sufficient fuel, water, oil and oxygen to function for 90 days without external help, CNN reported.

But in a "worst-case scenario," the missing sub could run out of oxygen in two days.

If the vessel is submerged and cannot raise a tube to the surface, the oxygen may only last for about seven days. Balbi said that when the sub last made contact on 15 November, it was submerged.

"This phase of search and rescue is critical," he said. "This is why we are deploying all resources with high-tech sensors. We welcome the help we have received to find them."

ARA San Juan:

The submarine's name is derived from the Argentine province of San Juan.

It was inaugurated in 1983, which made it the newest of the three submarines in the Argentine Navy's fleet. The vessel is 65 metres long and seven metres wide.

The submarine underwent a re-fit between 2007 and 2014 to extend its life by some 30 years.

It has a single-hull design, with a lightweight bow and stern and a watertight structure.

Its sister vessel, ARA Santa Cruz is the only other one of its type.