Photon Torpedoes are the primary faster than light, FTL, weapon used by Starfleet onboard starships and starbases. Photon torpedoes were first introduced into Starfleet service in 2215 to replace earlier photonic torpedoes and nuclear warheads.

Since their introduction there have been two primary torpedo designs. The first design was a 1:1 mater-antimatter explosive device. These torpedoes contained microfussion initiators that fired frozen deuterium slugs into magnetically suspended anti-deuterium. After briefly being held by the magnetic containment, the matter/antimatter annihilation energy was released powering the warhead. These first warheads had a maximum range of 750,000 km; even though powered by a matter/antimatter reaction, the warheads had a very low yield as there was not 100% annihilation. As a result these torpedoes were only used for defense purposes.

The current photon torpedo design is a variable matter/antimatter warhead design that was first introduced in 2271. In these new torpedoes the matter and antimatter are magnetically suspended in thousands of packets that increase the surface area of the reaction when the two mix. The resulting complete annihilation, when combined, multiplies the yield of the warhead to 18.5 isotons. The range of these new torpedoes has also increased to 4,050,000 km.

The standard Starfleet torpedo design consist of a 2.1 meter long elliptical enclosure containing deuterium and anti-deuterium storage tanks containing a maximum of 1.5 kilograms each; the storage tanks are connected to a central combiner tank. The torpedo casing also contains magnetic containment equipment, guidance and targeting systems, detonation assemblies, and a warp sustainer engine. If the ship is traveling at warp velocities, the warp sustainer engine is capable of transferring a ships warp field to the torpedo when fired to allow the weapon to move at FTL speeds; though it can not effectively increase the speed of the torpedo much beyond the ships original velocity. The sustainer engine is also not capable sending the torpedo into warp if the ship was traveling at impulse velocities when fired.

On Starfleet vessels there are normally one or two forward torpedo launchers and one aft launcher. Photon torpedoes are not stored on a starship armed with a full load matter and antimatter for safety reasons. When red alert is initiated, up to four torpedoes are fueled with matter and antimatter and loaded into the launching tubes; up to ten torpedoes can be loaded into the same launcher for simultaneous launch. When the command to fire is given, the ship's targeting computers transfers initial flight instructions to torpedo's computers. Shortly after launch the matter and antimatter are transferred to the central mixing tank though they are still kept separate by magnetic fields. While in flight the ship can transfer new targeting instructions to the torpedo to make in flight course corrections. Finally, one second before the torpedo reaches the target the magnetic fields are dropped allowing the matter and anti-matter to mix.

Photon torpedoes are currently being phased out of service in favor on quantum torpedoes aboard Starfleet vessels.