An explosion occurred near the time and place where the ARA San Juan disappeared Nov. 15. The navy says it is no longer looking for survivors although a multinational operation continues to search for the vessel, which had a crew of 44.
Navy spokesman Enrique Balbi said Russia's Yantar oceanographic research ship would arrive in the search area Tuesday. The U.S. Atlantis research vessel is expected to arrive Saturday. They are equipped with deep submergence vehicles that allow them to examine undersea areas nearly 20,000 feet deep (6,000 meters).
The ships will join five vessels from Argentina and a Chilean ship combing an area of some 1,500 square miles (4,000 square kilometers), where sonar detected three unidentified objects on the sea floor to see if they belong to the missing sub.
The San Juan disappeared as it was sailing from the southernmost port of Ushuaia to the coastal city of Mar del Plata after a patrol.
The navy has said the vessel's captain reported that water entered the snorkel and caused one of the submarine's batteries to short circuit. The captain later communicated by satellite phone that the problem had been contained, the navy says.
Some hours later, an explosion was detected near the time and place where the San Juan was last heard from. Balbi has said the blast could have been triggered by a "concentration of hydrogen" caused by the battery problem reported by the captain.
The German-built TR-1700 class submarine was commissioned in the 1980s and was most recently refitted between 2008 and 2014. It was built by a subsidiary of Germany's ThyssenKrupp that is no longer operational.
Balbi said a group of navy officials who traveled to Germany last week to obtain more information about the design of the submarine had returned to Argentina. He said they will submit all documents to a local judge investigating the sub's disappearance.
The spokesman said the information gathered in Germany as well as information from an Argentine submarine from the same model that is under repair at a state-owned shipyard could help provide evidence to find out what happened to the San Juan.
When asked if the refit of the submarine had been certified, Balbi said there are some processes that the Germany company might have been involved in and others where it was not.
"But of those things that it certified, surely there must be a record. Everything was duly registered and I imagine that all these reports made on the activation of batteries and repairs will be subject to investigation," he said, without providing more details.