Kronos One

In 2293, Kirk was to escort this Klingon battle cruiser, and Chancellor Gorkon, through Federation space to the Chancellor's peace meeting on Earth.

During the mission, Kronos One was attacked -- seemingly by Enterprise -- and had its artificial gravity disabled. The ship was then boarded by two assassins, wearing gravity boots, who proceeded to assassinate Chancellor Gorkon before beaming away.

Following the assassination, while under the command of General Chang, Kronos One turned about and locked its weapons on Enterprise, prompting Kirk to signal his vessel's surrender.