[ldiracdelta]

Bingo.

From my readings, the reason certain parts of shipping are mandated to be constructed in USA is that we Americans don't want to lose the ability to construct war ships. Tariffs may not be maximally efficient from a theoretical free trade perspective, but the cost premium of a tariff forcing local production may well be worth it compared to losing your ability to protect yourself on the seas.

Now, whether you agree with that sentiment or not is orthogonal. Chesterton's Fence says that if you don't understand why this law exists, then you don't get to tear it down until you do understand why it was ever thought to be a good idea.