Heavier-Than -Air Craft

[Grav_Moped]

Gravitic tugs pulling huge glider cargo transporters.

Antigrav self-launching sailplanes, especially if power generation capability is behind grav tech advancement.

 

[Proneutron]

Antigrav self-launching sailplanes, especially if power generation capability is behind grav tech advancement.

That would be low power required for sure

 

[BlackBat242]

One of my other favorite jets that did not make production, but would be highly useful on Water Worlds is the Saunders-Roe jet flying boat fighter.

https://en.wikipedia.org/wiki/Saunders-Roe_SR.A/1

That would have been handy down in the Falkland Islands as well.

Convair F2Y Sea Dart - supersonic jet ski/flying boat fighter.
https://en.wikipedia.org/wiki/Convair_F2Y_Sea_Dart

Then there is the Spruce Goose flying boat transport. Again, an aircraft that would be quite useful on a Water World. Give it eight Rolls-Royce Tyne turboprops, and you have a quite potent cargo carrier.

https://www.evergreenmuseum.org/the-spruce-goose

Convair R3Y Tradewind
https://en.wikipedia.org/wiki/Convair_R3Y_Tradewind

Jet multi-engine seaplane - Martin P6M SeaMaster
https://en.wikipedia.org/wiki/Martin_P6M_SeaMaster

Or its civil cargo-variant derivative, the SeaMistress:
https://www.secretprojects.co.uk/threads/martin-model-307-sea-mistress.6396/