Sharks attack submarine in terrifying Blue Planet II behind the scenes video

700 metres below the surface, the crew are filming a group of sixgill sharks as they devour a sperm whale carcass that has sunk to the ocean bottom.

Unfortunately for the crew, the sharks think that the submersible is a rival – and begin to aggressively butt their heads against the sub's viewing window.

The video below shows the six-metre-long animals repeatedly ramming the submersible; at one point one of the operators says, "The submarine is very strong, but they are so big and strong that I am a little bit afraid."

https://www.youtube.com/watch?v=Yn574acq9Fk&t=2s

Eventually, the sharks return to the whale carcass, seemingly realising that the sub is not a threat.

Before this week's episode, Blue Planet II producer Orla Doherty revealed to Radio Times that during one dive her submersible sprung a leak – but she carried on filming.

"The water was so cold one of the seals on a pressure gauge wasn’t absolutely sealed, so there was a small leak pooling at the bottom of the sub," she explained. "It never ripped or ruptured, but it certainly had our hearts beating pretty fast for 20 minutes while we tried to find it and stop it. That was definitely my most 'exciting' dive. We were very much at the point of no return, but we fixed the leak and we carried on."