The USS Fleming was a Federation medical transport that was in service to Starfleet in the late 24th century. It was constructed of such materials as duranium and poly-composites.
In 2370, the Fleming was transporting a cargo of bio-mimetic gel through the Hekaras Corridor when it was disabled by Hekaran scientists who were attempting to gain the attention of Starfleet.
The Fleming was later caught in a subspace rupture that had formed in the Corridor, where it had to be abandoned. Its crew was rescued by the USS Enterprise-D. (TNG: "Force of Nature")
The Star Trek Encyclopedia describes this vessel as a Wambundu-class starship, with a registry of NCC-20316.
The Fleming was named for Alexander Fleming, the doctor who discovered penicillin. (Star Trek: The Next Generation Companion)