So don't JIT. Just because it's cool doesn't mean it's a good fit in every case. Get a buffer stockpile and refill as needed.

The stuff you'd need to stockpile is unlikely to deprecate in value and it certainly isn't perishables, so doing so really isn't a big deal.

Also once you get an order you already know roughly how much steel you'll need - a bit of lag as you wait for the first batches to arrive really isn't a big deal in such a project.

Doesn't waiting mean union employees still getting paid and increasing costs in this industry?

If you don't assume that the drydock is sitting empty while the construction plans for the next ship are being thought up, while would it sit empty while you wait for supplies?

Presumably you'd get everything lined up before you finish your previous project. Hardly any construction just simply starts the day someone approaches a manufacturer anyways.