Buenos Aires, Argentina—An Argentine submarine is missing at sea.

ARA San Juan (S-42) was last heard off two days ago.  Since then, the 44-crew submarine has failed to respond to the Argentine military’s repeated communication attempts.

“We are investigating the reasons for the lack of communication. If there was a communication problem, the boat would have to come to the surface,” said Enrique Balbi, a navy spokesperson.

The submarine was heading from the city of Ushuaia, southern Argentina, to her home port in Mar del Plata, 1,800-miles to the north.