An Argentine submarine missing in the South Atlantic reported technical problems and had been ordered to port before vanishing.
ARA San Juan's last message reported a short circuit in its batteries and the vessel was ordered to return to its home, officials disclosed.
The Argentine Navy also quashed hopes that a series of brief incomplete satellite calls detected over the weekend could have been emergency calls from the vessel.
As the search dragged on, Buenos Aires was beginning to face domestic criticism for its handling of the search.
The submarine and its crew of 44 have now been missing for five days as a fleet of international vessels and patrol planes brave 6m waves and high winds to search hundreds of square kilometres.
US Navy submarine rescue chambers have been flown to the region in the hope of bringing the crew to the surface in case the vessel can be found.
Gabriel Galeazzi, a spokesman for the Argentine Navy, said the German-built diesel electric vessel had surfaced last Thursday to report the fault.
He said: "At that moment the commander was ordered to go directly to Mar del Plata. After that we lost contact."
He suggested the fault could have affected the submarine's navigation, but said it did have backup systems.
Although the crew has enough food, oxygen and fuel to survive about 90 days on the sea's surface, they only have enough oxygen to last for seven days if submerged.
After that, the boat would have to surface or get near the surface to replenish air supply.
Up to 20 vessels, including the Royal Navy's HMS Protector and HMS Clyde, are joining the search. Britain has also sent an RAF C-130 aircraft and a Voyager refuelling aircraft to help it search for longer.
Commander Erik Reynolds, spokesman for the US Navy, which is coordinating the international effort, said vessels were using their sonar to hunt for the ship, though high waves were hampering efforts. Maritime patrol planes are searching for signs of oil or waste that could have been jettisoned by the crew to signal their location.
Two US Navy undersea submarine rescue vessels are on standby if needed for a rescue. The vessels can attach to the hatch of a stricken submarine at depths of up to 600m and then ferry surviving crew back to the surface.
"There is no good news," Juan Carlos Mendoza, father of Fernando Mendoza, a crew member, told local reporters. "Hopefully they have oxygen."
Several submarines have vanished over the years, leaving mysteries that have lasted decades.
On May 27, 1968, the USS Scorpion failed to return to port, sinking 11,220 feet beneath the Atlantic Ocean along with its 99 crew members and two nuclear torpedoes, according to USA Today. A Navy inquiry concluded that the cause of the sinking "cannot be definitively ascertained." The cause remains fuzzy to this day.
Theories abound, of course: A torpedo self-fired into the ship, destroying it from the inside, or a battery exploded, inflicting critical damage. The Navy has routinely tested the water around the ship for radioactivity, according to USA Today, but has rejected a proposal by civilian marine disaster experts to investigate the wreckage.
In August 2000, the Russian nuclear submarine Kursk suddenly sank during a planned and closely monitored military exercise, killing all 188 sailors aboard, according to the New York Times. It was hours before the Russian government even knew something was amiss.
The most likely explanation was that fuel in a torpedo detonated, setting off a chain reaction in a sub once deemed unsinkable. The Russians have said the Kursk used an outdated and unstable hydrogen peroxide propellant.
Conspiracy theories emerged, and at least one real-life horror story was verified: Not all of the sailors died in the initial blast, according to the New York Times.
For hours, some fought fruitlessly to survive.
"13:15," Lt. Capt. Dimitri Kolesnikov, the commander of the turbine room, wrote, noting the military time. "All personnel from compartments six, seven and eight moved to the ninth. There are 23 of us here. We have made this decision as a result of the accident. None of us can get out."
- with Washington Post