Directive 010 was a Starfleet Command instruction (for engaging an alien opponent) in battle that was still active in the 24th century. Captain Kathryn Janeway quoted it verbatim when talking to Seven of Nine in 2375 while preparing to attack the "Terrasphere" created by Species 8472 to mimic Starfleet Headquarters.
The directive read (in part): "Before engaging alien species in battle, any and all attempts to make first contact and achieve non-military resolution must be made."
Despite the fact that USS Voyager had made contact with Species 8472 over a year ago and had barely gotten out of it alive, Janeway could not get the directive out of her mind, despite a suspicion that war was inevitable. (VOY: "In the Flesh")