Four manned descents and three unmanned descents have been achieved. The first was the manned descent by Swiss-designed, Italian-built, United States Navy-owned bathyscaphe "Trieste", which reached the bottom at 1:06 pm on 23 January 1960, with Don Walsh and Jacques Piccard on board. Iron shot was used for ballast, with gasoline for buoyancy. The onboard systems indicated a depth of , but this was later revised to . The depth was estimated from a conversion of pressure measured and calculations based on the water density from sea surface to seabed.