Battle of Donatu V
- Major conflict at Donatu V between United Federation of Planets and Klingon Empire (TOS: "The Trouble with Tribbles")
- First significant skirmish between the two powers (TOS: "The Trouble with Tribbles")
- Klingon Empire harried planet-side Federation colony as intrusion into Klingon space 2242 (TOS Novel: Errand of Vengeance: Killing Blow)
- USS Endeavor responded, was quickly destroyed by two battle cruisers in orbit (TOS Novel: Errand of Vengeance: Killing Blow)
- USS Yorkshire followed up upon receiving USS Endeavor automated distress signal (TOS Novel: Errand of Vengeance: Killing Blow)
- Shortly after second engagement, USS Constitution joined conflict (TOS Novel: Errand of Vengeance: Killing Blow)
- Further vessels joined, including two additional Klingon battlecruisers, two additional Federation starships (TOS Novel: Errand of Vengeance: Killing Blow)
- Results
- Significant losses on both Federation and Klingon sides (TOS Novel: Errand of Vengeance: Killing Blow)
- Klingons ceded territory to Federation
- Viewed as significant dishonor to Klingon Empire, laying groundwork for discontent driving both 2256 Federation-Klingon War and 2267 Federation-Klingon War