There exist many underwater vehicles that can withstand ocean pressures. The REMUS 6000 for example can reach depths of 6000m.

As the article describes, these are gliders:

> A glider is a small robot that slowly changes its buoyancy, becoming slightly heavier to sink and lighter to rise.

It doesn’t need battery power to endlessly spin a prop. With little energy expenditure it can inflate or deflate a bladder; changing volume changes buoyancy and therefore vertical motion in the water column. The vehicle’s design allows it to “soar” as it does so. The tradeoff is control.

It seems the vehicle they are using is the Alseamar SEAEXPLORER: https://www.alseamar-alcen.com/ocean-science-sector/seaexplo...