Earliest reference to Bushnell's submarine that I can locate is a presentation Bushnell made to the American Philosophical Society on it, in 1799, and is apparently in vol. IV of their transactions for that year.

An article was finally done on the Grasso/Frese replica in American History of Technology magazine much later, I think in the 90's( and I wish I had an index to that defunct magazine, so I could be more precise). They found that it was extremely hard to make it work: in order to submerge, it had to weigh more than the water it displaced. This gave it a a great deal of inertia and made human powering of it very difficult, so that when the operator tried to dive, it kept diving, and when aimed to the surface, it kept surfacing. This porpoising made level travel just beneath the water very hard , and could have been what drew the attention of the British soldiers standing watch on board their boats. This would also lend credibility to the theory of the British historian Compton-Hall, mentioned in the Wikipedia article, that it could simply not have worked. There's an interesting theory that Fulton got some- maybe most- of his ideas for his submarine from Bushnell and Lee. James Flexner pointed out the similarities, in Steamboats Come True, but more has likely been written on it. Fulton was quite happy to "borrow" ideas when it suited him. Since the defaulted submarine contract was what Fulton used to leverage the export license for a Boulton&Watt steam engine for his steamboat, from the British government, his American steamboat's success might be traced to Bushnell.