On Saturday, a U.S. plane and British ship have joined the hunt for a missing Argentine Navy submarine as concern grows over the fate of the 44 crew members on the vessel that officials believe is stranded in the San Jorge Gulf. The ARA San Juan submarine has not been heard from since Wednesday when it was last tracked some 267 miles off the coast on a routine security patrol; the country’s three subs are often used to combat illegal fishing, the New York Timesreports.

The Argentine government initially downplayed the severity of the sub going quiet, saying it could be the result of faulty communications equipment on the three-decade old submarine. The Argentine Navy said the sub has sufficient supplies of food and oxygen and that the protocol in a communications blackout is for the submarine to surface. As the length of time without communication with the craft stretched into Friday with the search effort slowed by high winds and 20-foot waves off the country’s Patagonia region, where the sub is thought to be, President Mauricio Macri escalated the response, calling for international assistance in locating the missing vessel. In response, a U.S. Navy P-8A Poseidon plane is expected to arrive in the country Saturday evening, a British ice patrol ship stationed in the Falkland Islands is expected to join the search Saturday, and a Chilean aircraft has been dispatched.

On board the sub is Argentina’s first female submarine officer, 35-year-old Eliana Krawczyk, according to Agence France-Presse.