Ship building.

[xoxoxoBruce]

Yes, keel+ribs+plates went out with sword fighting and knickers. During the Big One, WW II, the need for ships, and lot's of them, prompted US shipyards to build ships in sections, then join the sections together as drydock space became available.

Now big ships are a series of waterproof compartments joined together. Computer simulations verify the desired rigidity/flexibility for rough seas, plus damage control for various types of attacks.

To build that carrier in one spot would take either many, many years, or a labor force so large they'd have to recruit around the empire. Then when you break the champagne bottle and wave bye-bye, what do you do with that huge labor force that resettled into that community? For that matter what happens to the community that expanded to accept the huge, now unemployed, labor force?