I don't know if a "behemoth" of a merchant marine is required but a diminishing number of taxpayers are paying for it now. Since the bankers and money launderers discovered that they can make more money by selling off American industry rather than building it, a larger population now spends more of a shrinking income on foreign imports of products made by foreign industry and delivered to America by foreign ships.
Our own government seems to have no qualms about using foreign flag ships to carry cargo paid for by the taxpayer. MARAD owns a fleet of ships under the fiction of being prepared for defense needs. While those ships rot at the dock, foreign flag ships carry more taxpayer purchased government owned cargo.
We not only subsidize farmers to grow crops for giveaway programs, we pay foreign companies to deliver those products while American ships rot and mariners age out of the industry. That is among the most idiotic and stupid subsidies ever foisted on the non-farmer, non-money laundering, non-elected American.
Don't trash the "greens" for trying to protect the resources we still have. If not for them every tree in SE Alaska would be floating in a mill pond in Tokyo Bay. Talk about subsidies ... while timber companies were getting fat hauling publicly owned logs over Forest Service roads, those logs were shipped whole to Japan. The mills that used to employ Americans to process those logs were closed and the workers either "re-educated" at public expense or condemned to a life of unemployment or welfare. Who paid the bills for their medical care? Talk about subsidies ...
If our corrupt politicians and MARAD weren't bent over by the bankers and thieves who bought them the office we might have a healthy merchant marine based on a healthy economy that can support domestic production and transportation.
Talk about subsidies? Look at what we spend to promote and support the cruise industry and the foreign yards that profit by it.
We are rapidly becoming one of the largest kleptocracies on the planet.