Simon Boxal, an oceanologist who teaches at the University of Southampton, said the crew aboard the missing vessel sent out an “emergency ping.”

“This is second-hand knowledge but my understanding is that they have received a signal from the submarine,” Boxal told PA News, according to The Independent.

Boxal added he didn’t know the timing of when the signal went out.

“I don’t know if that is automatically generated or generated by people on board,” he said.