In 2155, an assault fleet which included the ISS Enterprise (NX-01) was a fleet of Starfleet combat ships which fought in an ongoing war, in the mirror universe, against the rebellion. (ENT: "In a Mirror, Darkly")
The assault fleet was destroyed by a rebel attack. Only the ISS Avenger survived. (ENT: "In a Mirror, Darkly, Part II")
During the closing weeks of the Dominion War in 2375, a Federation assault fleet was assembled to stop the Dominion and the Breen from driving the Federation Alliance out of the Chin'toka system. The assault fleet was unsuccessful in stopping the enemy from retaking the star system, as all of the ships, except the IKS Ki'tang, were disabled by the Breen's energy dissipators. (DS9: "The Changing Face of Evil", "When It Rains...")