What true event inspired Herman Melville to write his epic novel, 'Moby Dick'?

The Essex was a Nantucket, Massachusetts whaler launched in 1799. It departed Nantucket on its final voyage August 12,1819.

November 20, 1820, in the South Pacific, Essex encountered a pod of whales during a heretofore prosperous voyage, and while the small boats were being dragged out toward the horizon in what the crew called “Nantucket sleigh rides” by whales, First Mate Owen Chase spotted a huge sperm whale- estimated 85 feet in length, as long as the Essex herself - lying quietly in the distance, its head facing the ship. Then, after two or three spouts, the giant made straight for the Essex at about three knots, as Chase recalled. The whale met the Essex head-on, smashing a hole in the bow - then circled and came at the ship a second time at six knots. The resulting hole let the water rush into the ship so fast that the Essex rolled onto its side in a matter of minutes.

All 20 crewmen survived in three boats initially, but they were weeks away from the nearest islands, the Marquesas. On Chase’s boat, one man went mad before perishing the next morning. Being completely out food or supplies, the desperate men cut their dead shipmate up and ate him.

Enduring madness, a scorching sun, and more cannibalism in the face of starvation, the three boat crews, having lost sight of each other, were separately rescued. Only eight survived.

The book and subsequent movie 'In the Heart of the Sea' (2015) tells the harrowing story of the survivors of the Essex.