The first link is a good overview article. The second is an informal history of America’s merchant marine service. The third covers the pros and cons of supertankers. The fourth critiques Trump’s vanity project of wanting to build the biggest, bestest battleship ever.
Reading these won’t necessarily lead to investing insights into an industry that’s outside the ken of most people. But America was once --and probably still is-- an important maritime power, no matter its current indulgence in a bit of high seas piracy.