Moncrief-class transport/tugs on active duty in Starfleet during at least the 23rd century. The class was authorized in July, 2266. ((Jackill's Starfleet Reference Manual: Ships of the Fleet, vol. 1, 2006 revision)USS Moncrief (NCC-3800) was the lead ship and prototype for the
In the mid- to late 2260s, Moncrief would undergo successful trials but Ptolemy-class ships would not be refit — nor new-build ships constructed — until linear warp drive was tested on vessels such as the Decatur, Intrepid and Enterprise.