Trekipedia

U.S.S. Lexington NCC-1709

The Constitution class Starship Lexington, commanded by Commodore Robert Wesley, participated in the disastrous tests of the M-5 multitronic computer. During those tests, the multitronic unit malfunctioned and fired full phasers on the Lexington, killing 53 people on that ship, as well as the entire crew of the U.S.S. Excalibur NCC-1664.^[1]

Lieutenant Watley, presumably an ancestor of Deep Space 9 chief medical officer Julian Bashir, transferred from the Lexington to the U.S.S. Enterprise NCC-1701 a few months before the M-5 tests, and unknowingly met her descendant while the Enterprise was at Deep Space K-7 in 2268.^[2]