A Pacific storm and difficult winds diverted Challenger north during its 1875 passage toward Japan. Rather than suspend the programme, the crew continued sampling and recorded 4,475 fathoms at station 225 on 23 March 1875, more than eight kilometres deep. They repeated the sounding because unusually deep results required confirmation. A weighted marked rope and celestial navigation located the station only to within roughly two nautical miles. This early success contrasts with Sirena Deep, about 115 nautical miles east and identified only in 1997.
Chapter · 34:21-38:25
Finding Challenger Deep after a storm diversion
Storm-driven route changes led Challenger to the Mariana region, where repeated soundings recorded the depth later known as Challenger Deep.