We're hooked on ground-breaking nature series Blue Planet II, which took over four years to make, involved 125 expeditions, visits to 39 countries, and 4,000 dives that clocked up 6,000 hours spent underwater. We've seen bird-eating fish, surfing dolphins and had a stunning look at what lies beneath in the deepest, darkest oceans. To get the astonishing footage, the Blue Planet II team used the latest technology and even created their own specialist equipment to capture new landscapes and previously undocumented animal behaviour. Here we look at some of the tech that has given us a new look at the oceans.