Piloting the bathyscaphe Trieste, they descended into the Mariana Trench, the deepest point of the oceans, reaching a record depth of 10,916 metres (35,814 feet).

Attached to the submersible’s exterior, an experimental Rolex watch, the Deep Sea Special, withstood the colossal pressure of more than one tonne per square centimetre and returned to the surface in perfect working order. Piccard telegraphed Rolex with the following message: “Glad to report your watch as accurate at 11,000 metres [6.8 miles] as on land. Best wishes.”