|Battle of Krypton|
The Battle of Krypton was the first contact between the Lyran Star Empire and the Borg Collective. It ended with a Borg defeat, but not without a material cost to the Lyran Starfleet. (RIS Bouteina: "Sphere of Influence")
The Romulans, sensing a Borg probe over Krypton (and presumably detected by the Lyrans as well) while surveying the planet, fought the Borg back, exploiting a moment of weakness into the Borg's defenses, destroying the probe. It was later found that a larger Borg force was to fly through the Krypton system. Thus the Lyran Starfleet assembled a fleet out of Starbase 47 to engage the Borg fleet, Senior Commodore Pfrizzek being placed in command.
At first, the Lyrans started fighting the Borg Spheres, having already lost three ships before the Tal Prai'ex entered the fray. Just as they entered the scene, a Lyran military police cutter was being tractored and they seized the occasion to ram the enemy with expanding sphere generators, putting dents at first and later sacrificing the cutter.
And, much later, the Borg ships adapted to the expanding sphere generators while not having adapted to the photon torpedoes yet, leading to the loss of the first Borg sphere but not the flagship of the Borg fleet dispatched to the area. However, once the Borg adapted to the photon torpedoes, the Romulans started using the quantum torpedoes, with not much success, until they used phased plasma torpedoes, which finally allowed the Romulans to defeat the Borg flagship, a Borg tactical sphere called Sphere 911.
Because of their involvment in the defense of the Lyran Star Empire against the Borg, the Lyran Star Empire inadvertantly pit the Romulan Star Empire against the Kzinti Patriarchy, for the Bouteina was granted the permission of using Lyran shipyards at Starbase 47 (Lyran) in exchange for Romulan help against the Kzintis. The survivors of the battle were assigned all the holodecks inside Starbase 47 for a day. (RIS Bouteina: "Broken Bread")