At least 14 Russian Navy servicemen died on Wednesday after a scientific deep submersible caught fire while taking biometric measurements, RT reported quoting the defence ministry.

A deep-water research apparatus belonging to the Russian Navy was conducting a bathymetric measurement operation in Russian territorial waters when a fire broke out on board, the defence ministry’s statement said.

The cause of the incident is under investigation. Russian Navy Chief Nikolay Efimov took the matter under his personal control.

The vessel was based at Severomorsk, in the country’s northwestern region of Murmansk, which is the main base of the Northern Fleet, BBC reported.

The 14 seamen were reportedly suffocated by smoke. The crew, however, managed to extinguish the flames. The deep submersible returned to the Russian Navy base after the incident, according to RT.

A submersible is an underwater vessel that usually requires a support ship on the surface. A submarine, on the other hand, is fully autonomous.