By Rebecca Morelle, Science correspondent, BBC
The first people to dive down to the Titanic in nearly 15 years say some of the wreck is deteriorating rapidly.
Source: BBC News
Over the course of five submersible dives, an international team of deep-sea explorers surveyed the sunken ship, which lies 3800m down in the Atlantic.
While parts of the wreck were in surprisingly good condition, other features had been lost to the sea. The worst decay was seen on the starboard side of the officers' quarters.
Titanic historian Parks Stephenson said some of what he saw during the dive was "shocking".
"The captain's bathtub is a favourite image among Titanic enthusiasts - and that's now gone," he said.
"That whole deck house on that side is collapsing, taking with it the state rooms. And that deterioration is going to continue advancing."
He said the sloping lounge roof of the bow section would probably be the next part to be lost, obscuring views of the ship's interior.
"Titanic is returning to nature," he added.
Strong ocean currents, salt corrosion and metal-eating bacteria are attacking the ship.
The RMS Titanic has been under water for more than 100 years, lying about 600km (370 miles) off the coast of Newfoundland, Canada.
The passenger liner, which was the largest ship of its time, hit an iceberg on its maiden voyage from Southampton to New York in 1912. Of the 2200 passengers and crew onboard, more than 1500 died.
The Titanic expedition was carried out by the same team that recently made the deepest-ever plunge to the bottom of the Mariana Trench, which lies nearly 12km down the Pacific Ocean.
The dives took place in a 4.6m-long, 3.7m-high submersible - called the DSV Limiting Factor - which was built by the US-based company Triton Submarines.
Navigating the sub around the wreck, which lies in two main pieces about 600m apart, was challenging.
Bad weather in the Atlantic and strong underwater currents made the dives difficult. Getting entangled with the wreck was also a significant risk for the team.
- 1912 - Titanic, world's largest ship at the time, sinks
- 1985 - Titanic site discovered by American-French team
- 1986 - Submersible Alvin explores wreck
- 1987 - First salvage expedition collects 1800 Titanic artefacts
- 1995 - Film director James Cameron visits the wreck - footage is used in his film Titanic
- 1998 - First tourists dive there
- 1998 - Section of the Titanic hull is raised
- 2005 - Two crewed submersibles dive to the wreck
- 2010 - Autonomous robots map the site
- 2012 - Wreck now protected by Unesco
- 2019 - DSV Limiting Factor sub makes five dives
The dives have been filmed by Atlantic Productions for a forthcoming documentary.
As well as capturing footage, scientists on the expedition have also been studying the creatures living on the wreck.
Despite the near-freezing conditions, pitch black waters and immense pressure, life is thriving there. Expedition scientist Clare Fitzsimmons, from Newcastle University, said it was a factor in the Titanic's decay.
"There are microbes on the shipwreck that are eating away the iron of the wreck itself, creating 'rusticle' structures, which is a much weaker form of the metal," she said.
These rusticles - stalactites of rust hanging off the wreck - are so fragile that they can crumble into a cloud of dust if disturbed.
The scientists are studying how different types of metal erode in the deep Atlantic waters, to assess how much longer the Titanic has left.
Commenting on the expedition, Robert Blyth from the National Maritime Museum in Greenwich said it was important to go down and document the wreck in its current state.
"The wreck itself is the only witness we've now got of the Titanic disaster," he said.
"All of the survivors have now passed away, so I think it's important to use the wreck whilst the wreck still has something to say."