Endurance just before it sank: Crushed at the stern, it went down bow first. Photo/RGS
Antarctic scientists seeking to locate the wreck of Sir Ernest Shackleton's lost ship, the Endurance, have arrived at the search site.
The team broke through thick pack-ice on Sunday to reach the vessel's last known position in the Weddell Sea.
Robotic submersibles will now spend the next few days scouring the ocean floor for the maritime icon.
Shackleton and his crew had to abandon Endurance in 1915 when it was crushed by sea-ice and sank in 3,000m of water.
Their escape across the frozen floes on foot and in lifeboats is an extraordinary story that has resonated down the years - and makes the wooden polar yacht perhaps the most sought-after of all undiscovered wrecks.
The SA Agulhas II will have to keep holes in the sea-ice open to operate the subs. Photo/WEDDELL SEA EXPEDITION 2019
Operating from the South African ice-breaker, the SA Agulhas II, the team's plan is to put down an autonomous underwater vehicle (AUV) to map the seafloor for anomalies.
A wide box has been designated, and the robot, equipped with side-scan sonar and other technologies, will run back and forth across this search zone like a lawnmower. The first dive, initiated on Sunday, will last roughly 45 hours.
There will be no attempt to retrieve artifacts should the Endurance be found. The intention only is to make a 3D model of the wreck site and take photos.
"The autonomous vehicle has a number of different sensors, ranging in resolution from about 10m down to about half a meter. And it also has cameras. It's not going to be as crisp as the image you or I might take - but almost as good as that," expedition chief scientist Prof Julian Dowdeswell told BBC News.
The search will be challenging because of the sea-ice at the surface. The Agulhas will have to periodically shift its hull to maintain open holes in the floes, through which to launch and recover AUVs.
Prof Dowdeswell emphasized: "The robot has to be recovered by the parent vessel [before the data can be] interrogated. And the difficulty with this is that in severe sea-ice conditions - it's not that easy to recover the autonomous underwater vehicle. That is an act of seamanship in itself - before the data can be looked at."