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. Shackleton's skipper, Frank Worsely, was a very skilled navigator and used a sextant and chronometer to calculate the precise co-ordinates of the Endurance sinking - 68°39'30.0" South and 52°26'30.0" West.