On board Norway's giant underwater gas platform
5 August 2013 Last updated at 10:49 BST
A structure the size of a football pitch has been sent plunging to the bottom of the ocean, 125 miles off the coast of Norway.
It will house a giant compressor claimed to be the world’s biggest offshore machine.
The Statoil equipment has been designed to pump some £20bn ($30bn/23bn euros) worth of gas from a depleted gas field.
It is a technological leap for Statoil to place the compressor on the sea bed instead of on a typical platform perched above the waves.
Roger Harrabin got a view from the compressor platform before it was sunk.