WE ALL RELIED ON A YELLOW SUBMARINE

I’m drifting in the Gulf of Mexico, with about two miles of water below me, waiting to glimpse a yellow submarine. The nearest land is New Orleans, about 300 miles away. There’s no better way to understand the vastness of the ocean than to be fully immersed in it, free of walls and vulnerable to its every whim.

The first I see of the Johnson Sea Link submersible (left) is the silvery stream of bubbles in the water below. Then the sub rises past me. Stubby and small, it is huffing and puffing like a steam engine. Though it is one of the technological miracles of the 20th century, it is too cramped to include a toilet for the four people inside.

The fans of its vertical thrusters are turning slowly. As I film, the sub purges its air tanks and begins to sink again. It is 1999 and this shot will become one of the first scenes of Blue Planet. I wonder whether, today, the guardians of health and safety would allow a film crew to float in the open sea with the chance of being run over by 12 tons of yellow steel and getting chewed in its thrusters.