An Ambassador-class Federation starship that fought beside the USS Saratoga against the Borg cube at Wolf 359 in 2367 and was destroyed in the battle.
The USS Yamaguchi was an Ambassador-class starship, the same class as the Enterprise-C. It is seen in the opening minutes of Emissary, the first episode of Deep Space Nine, which shows the Battle of Wolf 359 from the bridge of the USS Saratoga.
In that sequence the Yamaguchi moves in to attack the Borg cube together with the Saratoga, the Melbourne and other ships. The cube tears through the formation in moments and the Yamaguchi is lost with the rest of the fleet.
The ship is not named in dialogue; its name and the registry NCC-26510 come from the lettering on the studio model, so the registry is recorded here but left out of the title.