"Thomas Washington" returned briefly to the Challenger Deep on 17–19 October 1978 during "Mariana Expedition Leg 5" under chief scientist James W. Hawkins. The ship tracked to the south and west of the eastern basin, and recorded depths between to . Another miss. On "Mariana Expedition Leg 8", under chief scientist Yayanos, "Thomas Washington" was again involved, from 12–21 December 1978, with an intensive biological study of the western and central basins of the Challenger Deep. Fourteen traps and pressure-retaining traps were put down to depths ranging from to meters, the greatest depth was at . All of the 10,900-plus m recordings were in the western basin. The depth was furthest east at 142°26.4' E (in the central basin), about 17 km west of the eastern basin. Again, focused efforts on the known areas of extreme depths (the western and central basins) was so tight that the eastern basin again was missed by this expedition.