> the only way the US Navy succeeded was by using a huge amount of resources under tight top-down control.

Everything in the military is done with tight top down control for the most part. That's not why it succeeded, though. The military is the only organization that did it since it's the only organization for which nuclear wasn't constrained by the need for profit.

There was a demonstration nuclear cargo vessel built that operated for four years, but they weren't mass produced and so weren't economically viable when oil was cheap.

However, if you combine the need for lowered emissions with the higher modern price of oil, larger scale production of nuclear civilian vessels begins to make some economic sense.

This is aided also by the fact that modern reactors could be designed to be lower cost to operate.

Security wise, nuclear powered vessels would be less vulnerable than oil powered vessels presently are because they'd be at least as fast and would need refueling less often.

They would not be a more attractive target for terrorists than other ships despite nuclear propulsion, because the reactors can be designed to be tamper proof, meaning the only thing a terrorist in possession of a nuclear ship can do is sink it with little resulting fear or hardship for the country they are trying to affect. Water blocks radiation very effectively, and ships with sunken nuclear reactors don't spread radiation around, they contain it.

Having one of these ships sink is not as terrible as you might think. Water is an excellent moderator and these very heavy elements will tend to stay on the ocean floor. There's a reason we store nuclear waste in big swimming pools.