Warship refueling at sea - GIFs

[Drew1966]

This strikes me as an unnecessary drill. Why not just land the bird on the deck and then refuel.

[Jon]

Best guess is that they're practicing.

[Drew1966]

It’s really only worth doing a “hot” refuel if it’s too dangerous to land the hopcopter. (That’s what my favourite nephew always called ‘copters)

[Frank S]

I would say that both Jon and drew 1966 are correct this would have been a practice drill for times when it is too dangerous to land.
Just like replenishing ammo in tanks while underway or on battle station practice makes perfect for the times when seconds and lives are on the line. You would no more go into battle with a broken firing pin in your M4 and not know how to strip it in the field than you would fly a jet or a helicopter with not knowing how to refuel by every means available to you

[Jon]

Vapor cones forming around an aircraft during mid-air refueling.



2:39 source video:

More: https://en.wikipedia.org/wiki/Vapor_cone