- These dates would correspond to the early 2250s on the standard timeline. While a long-term conflict with the Klingons seems contradictory to the events of Star Trek: Discovery, it could be rationalized that this was possibly a highly localized conflict, and/or a conflict with a particular racial or political sect of Klingons that is set apart from the warring Klingon Houses of T'Kuvma's later military action. It is also possible that a divergence of an alternate reality is involved, however no source yet describes any logical explanation for any such divergence, as all related sources are intended to be in the prime reality of Star Trek.
The war started when the Federation colony on Archanis IV was attacked which resulted in the death of 112 Federation citizens. It was discovered later that the Federation protectorate world of Axanar served as a base for a Klingon garrison. This was discovered when Captain Garth of the USS Xenophon encountered a disabled Klingon cruiser inside Federation space. Admiral Kkorhetza of the Klingon garrison declined the opportunity to surrender the garrison to Starfleet, which started the war. (FASA RPG module: The Four Years War)
The Four Years War caused a military buildup between the Klingon Empire and Federation, resulting in numerous advances in starship technology. The following classes saw action in this conflict:
- Achernar-class • Baton Rouge-class • Constitution-class • Heston-class • Tikopai-class • Anton-class • Canopus-class • Apache-class • Larson-class • Marklin-class • Monoceros-class • Portsmith-class • Siva-class • Loknar-class • Fenlon-class • Bode-class • Hale-class • Hermes-class • Nelson-class • Sawyer-class • Chariot-class • Dollond-class • Kepler-class • Ptolemy-class • Cochrane-class • Aakenn-class • Liberty-class • Eagle-class • Cygnus-class