The 2373 Borg attack on Earth, seen in Star Trek: First Contact, in which the Enterprise-E joined the fleet.
Six years after the disaster at Wolf 359, the Borg returned to Federation space with a single cube bound directly for Earth. Starfleet had been preparing for this since the earlier attack, and a large defensive fleet was assembled in Sector 001, the region around Earth and the Sol system.
The fleet engaged the cube and was losing badly when the new Enterprise-E arrived. Captain Picard, who had been kept out of the fight because of his past as Locutus, disobeyed orders, took charge and directed the ships to concentrate fire on a vulnerable point in the cube. The cube was destroyed, but it launched a sphere before it died, and the sphere traveled back through time to the twenty-first century.
The Enterprise followed the sphere into the past, setting up the events of First Contact. Picard, Riker, Data, Worf, Troi, Crusher and La Forge all played roles, and the Defiant, commanded by Worf, also fought in the battle. The engagement allowed Starfleet to survive and showed how the lessons of the first Borg attack had changed its tactics.