The Merrimac participated in several transport missions, including ferrying Ambassador Sarek and his entourage back to Vulcan in 2366 and Cadet Wesley Crusher back to Starfleet Academy in 2368. (TNG: "Sarek", "The Game")
It also embarked on special missions, including working with the Vulcan Science Academy in 2366 and as part of a blockade the Romulan-Klingon border against Romulan forces during 2368's Klingon Civil War. (TNG: "Brothers", "Redemption II")
- As there is a Defiant-class USS Merrimac, it would be assumed the Nebula-class Merrimac is no longer in service.