An Argentine military submarine reported an electrical problem and was headed back to base when it went missing last week in the South Atlantic, the navy said on Monday, while storms complicated efforts to find the vessel and its 44 crew members.

Hopes for a successful search for the ARA San Juan submarine, which went missing last Wednesday off the Argentine coast, waned on Monday when the navy said satellite calls detected over the weekend did not in fact come from the vessel.

More than a dozen boats and aircraft from Argentina, the United States, Britain, Chile and Brazil joined the search effort. Authorities have mainly been scanning the sea from the sky, as storms have made it difficult for boats.

Gabriel Galeazzi, a naval commander, told reporters that the submarine had surfaced and reported an electrical malfunction before it disappeared 432 km off the coast.

An Argentine national flag with messages in support of the 44 crew members of the ARA San Juan submarine missing at sea is seen placed on a fence at the Argentine Naval Base where it sailed from, in Mar del Plata, Argentina November 20, 2017. Words on the flag read “With the crew of the ARA San Juan submarine, may God and our homeland keep accompanying you”. (Photo: Reuters)

“The submarine surfaced and reported a malfunction, which is why its ground command ordered it to return to its naval base at Mar del Plata,” he said.

Galeazzi said it is normal for submarines to suffer system malfunctions. “A warship has a lot of backup systems, to allow it to move from one to another when there is a breakdown,” he said.

Crew members’ relatives gathered at the Mar del Plata naval base, waiting for news. They were joined by President Mauricio Macri, who arrived late morning but did not address the media.

Intermittent satellite communications had been detected on Saturday and the navy had said they were likely to have come from the submarine. But the ARA San Juan in fact sent its last signal on Wednesday, navy spokesman Enrique Balbi said.

A man poses for a photo in front of an Argentine Naval Base, where the missing at sea ARA San Juan submarine sailed from, in Mar del Plata, Argentina November 19, 2017. REUTERS/Marcos Brindicci

The calls that were detected “did not correspond to the satellite phone of the submarine San Juan,” he said on Monday, adding that the craft had oxygen for seven days. After that, he said, it would have to surface or get near the surface to replenish air supply.

“There is no good news,” Juan Carlos Mendoza, father of crew member Fernando Mendoza, told reporters. “Hopefully they have oxygen.”

The ARA San Juan was inaugurated in 1983, making it the newest of the three submarines in the navy’s fleet. Built in Germany, it underwent maintenance in 2008 in Argentina.

That maintenance included the replacement of its four diesel engines and its electric propeller engines, according to specialist publication Jane’s Sentinel.

Reuters