Marine contractors have begun sinking the decommissioned ocean liner United States off Okaloosa County, Florida, to create an artificial reef and diving site.
Deployment began at approximately 13:40 local time at a site around 22 nautical miles southwest of Destin-Fort Walton Beach in the Gulf of Mexico. All valves had been opened shortly before 17:00.
At 17:47, officials described the ship as fully flooded, with the deployment still continuing. At that stage, the liner had not been confirmed as resting on the seabed.
The operation uses controlled flooding. County spokesperson Nick Tomecek said federal environmental and explosives rules prevented the use of explosives.
Workers removed tanks fed by the boiler-cooling seawater pipes so that the open valves would admit water into the hull. They also cut openings through the decks and removed more than 400 portholes.
The county's plan calls for the vessel to settle upright at a depth of 180 feet (55 metres), with approximately 55 feet (17 metres) of water above the upper deck.
The US Coast Guard directed other vessels to remain at least one nautical mile from the liner until the sinking is complete.
Survey divers will inspect the ship's position and condition before the site opens for recreational diving, according to X-Ray International Dive Magazine. Compartments deemed unfit for divers were closed off during preparation.
The vessel holds a 10-year re-authorisation permit from the US Army Corps of Engineers. Post-deployment monitoring is being developed with Woods Hole Oceanographic Institution, Dauphin Island Sea Lab, and Louisiana State University.
The sinking had originally been scheduled for November 12. County officials brought it forward because of forecast wind and sea conditions.
The 990-foot (300-metre) liner left Mobile, Alabama, under tow on Monday, November 9.
