After the USS Enterprise was badly damaged attempting to scan the red bursts in 2257, two Federation tugs were dispatched to tow her to a repair facility. Captain Christopher Pike and Commander Michael Burnham watched the tugs from the USS Discovery, discussing the nature of her distant relationship with her foster-brother Spock. (DIS: "Brother")
The Federation tug was constructed by using the primary hull from the Malachowski-class, the nacelles from the Hoover-class, and the pylon components from the Walker-class, combined with a number of newly-built parts as seen in the graphic to the left.
The tugs seen on-screen in "Brother" and "Children of Mars" did not have registries or names rendered onto their hulls. Alex Kurtzman assigned the name "USS Zimmerman" (NCC-1616) for the model for the Star Trek: Discovery The Official Starships Collection, following a request by Eaglemoss Collections' Ben Robinson and CBS' John Van Citters. 
The Star Trek: Discovery The Official Starships Collection lists this as a Helios-class ship.