A photon torpedo is a torpedo weapon armed with an antimatter warhead. Enterprise episode Sleeping Dogs reveals that the Klingons have had photon torpedo technology since as early as 2151. Photon torpedoes first appear on a Starfleet ship in the Original Series episode Arena as part of the USS Enterprise's armament.

The key ships and installations in subsequent Star Trek spin-offs, other than Star Trek: Enterprise, are also armed with photon torpedoes.Photon torpedoes appear as red, orange, yellow or blue blobs of light when fired.


Furthermore, smaller Starfleet craft such as shuttlecraft and Runabouts can be armed with 'micro-torpedoes', a scaled-down version of photon torpedoes designed for use on craft too small to accommodate the full-sized torpedoes.