The movie is based on the true story of the whaleship Essex, which was attacked by a massive sperm whale on November 20, 1820. The Essex was a Nantucket-based whaling ship that set sail in August 1819. The crew of 21 men was led by Captain George Pollard Jr. and first mate Owen Chase. The ship was on a voyage to the Pacific Ocean to hunt sperm whales, which were highly valued for their oil.

The ordeal that followed was one of the most harrowing in maritime history. The crew faced starvation, dehydration, and exposure to the elements. They were forced to resort to cannibalism to survive, eating the flesh of their dead companions to sustain themselves. Only eight men survived, and they were rescued after 83 days adrift.

After 15 months at sea, the Essex encountered a massive sperm whale about 1,500 miles west of the Galapagos Islands. The whale attacked the ship, causing significant damage, and the crew was forced to abandon ship. The survivors, including Chase and Pollard, were left to fend for themselves in small boats, with limited supplies.