Do you want to talk submarines?
I think the era of carbon fiber subs is over, taking a place alongside screen doors.
GRXD-810: This is a nanoscale 3D printed metamaterial. 1000x as strong as steel.
Relativity Space: They 3D print fuel tanks for space ships, doing a vase-mode print on a turntable.
Combine the two and you'd be able to make a sub as big as a school bus.