Moby Dick is inspired by the case of the whaleship Essex, a Nantucket whaleship that was sunk by a whale in 1820. Of the twenty man crew, seven died at sea and were cannibalized by the survivors.

Ahab is a loose interpretation of Captain George Pollard Jr., who would go on to be a night watchman on Nantucket after sinking a second ship (in a more conventional way!), but this is more an effect of Pollard's position, not his personality.

The first mate, Owen Chase, published the remarkable account the following year (after having been lost at sea 89 days). Chase's Narrative of the Most Extraordinary and Distressing Shipwreck of the Whale-Ship Essex explores how the crew responded to the incident and the decisions made at sea. He describes the whale strike:

I observed a very large spermaceti whale, as well as I could judge, about eighty-five feet in length; he broke water about twenty rods off our weather-bow, and was lying quietly, with his head in a direction for the ship. He spouted two or three times, and then disappeared. In less than two or three seconds he came up again, about the length of the ship off, and made directly for us, at the rate of about three knots. The ship was then going with about the same velocity. His appearance and attitude gave us at first no alarm; but while I stood watching his movements, and observing him but a ship’s length off, coming down for us with great celerity...he came down upon us with full speed, and struck the ship with his head, just forward of the fore-chains; he gave us such an appalling and tremendous jar, as nearly threw us all on our faces. The ship brought up as suddenly and violently as if she had struck a rock...

I could distinctly see him smite his jaws together, as if distracted with rage and fury. He remained a short time in this situation, and then started off with great velocity, across the bows of the ship, to windward...He struck her to windward, directly under the cathead, and completely stove in her bows...

Owen's account, unsurprisingly, paints his actions positively. Thomas Nickerson, who was just 14, wrote an account at the end of his life that examines the conflicts between Chase and Pollard: the former an overeager upstart who questioned Pollard's authority, the latter too meek to rule authoritatively (Greg Dening's Mr. Bligh's Bad Language is a wonderful case study of how difficult maintaining power properly is at sea). The crew had the option of sailing west, but chose to sail east due to fear of cannibals on the South Pacific islands (the irony not being lost in Melville's interpretation).

The Essex was a remarkably alluring story - of nature's revenge, of mismanagement in crisis, of human ingenuity and accomplishment in the face of disaster - and was one of the most famous seafaring incidents of the century.

The Essex's fame is in part due to the uniqueness of the whale attack, though. Right before Moby Dick was published, the Ann Alexander was similarly charged and sunk by a sperm whale in 1851; unlike the Essex, the crew were recovered just a few days later. There is certainly truth to whales attacking and sinking ships, but they are very rare.

Nathaniel Philbrook's In the Heart of the Sea is a great read that dives into the Essex; at times it is probably too conjectural, but it's nonetheless worth reading. Nickerson and Chase's accounts are certainly worth reading as well, with similar caveats for framing and, for Nickerson, timing.