Star Trek: 12 Biggest Losses Starfleet Ever Faced
8. Wolf 359
Although Starfleet would incur greater losses in the battles that would come in the years that followed, Star Trek was utterly changed forever by the Battle of Wolf 359, Starfleet's first large scale encounter with the Borg. This was also of course the assault that was led by Locutus of Borg, which would forever have a lasting effect on Captain Picard.
Star Trek had spoken about war before. The Original Series had let the audience know of a Romulan war that had preceded the show, while in continuity, the Cardassian border wars had only recently finished by the time of the Borg incursion.
However, in both of those examples, Starfleet was somewhat evenly matched. The Borg carve their way through Starfleet on their way to Earth, with a total of 39 starships and 11,000 lives lost in the fight.
The battle was largely off-screen, though there was a quick, traumatic depiction in Emissary, the Deep Space Nine pilot episode.