The Original Series (TOS), red bolts. According to the original notes to TOS and The Making of Star Trek, photon torpedoes are energy shielded to allow armor-penetration. Several episodes seem to suggest this (TNG: "Suspicions"). The energy output of a photon torpedo, according to the Star Trek Technical Manuals is a maximum theoretical yield of 25 isotons and a maximum rated yield of 18.5 isotons. According to Star Trek: The Next Generation Technical Manual, photon torpedoes use of matter and the same amount of antimatter. In the TOS episode, "Balance of Terror", photon torpedoes apparently replaced nuclear warheads as the primary wartime weapons on Federation starships. Assuming a 100% mass-to-energy conversion ratio, reacting 1.5 kg of matter with 1.5 kg of antimatter would release the equivalent of 64.442 megatons of TNT, similar in scale (albeit slightly more powerful) to the Tsar Bomba. Torpedoes are often depicted as being easy to modify to suit specific situations. Despite the stated maximum yield, torpedoes can apparently be made far more destructive with relatively little effort. In Star Trek: Voyager, Tuvok and Kim modify a normal photon torpedo with a gravimetric charge, a piece of Borg technology, to increase its destructive yield to 54 isotons. Kim comments that 50 isotons would have been sufficient to destroy a small planet. Janeway later instructs them to increase its yield even further, to 80 isotons. It is not specified exactly how they modified the warhead, but they only required a few hours to complete the work using materials readily available on Voyager. In Star Trek VI: The Undiscovered Country, Spock and Dr. McCoy modify a photon torpedo to track the plasma emissions from a cloaked Klingon bird of prey as it attacks the Enterprise-A and the Excelsior, similar to the principal function of the heat-seeking missile. Photon torpedo launchers aboard ships are shown to be versatile enough to fire probes, which, in-universe, are designed with this functionality in mind. In Star Trek II: The Wrath of Khan, a torpedo casing is used as a makeshift coffin for burial in space and as scientific probes as in the TNG episode "In Theory" and in Star Trek Generations. Plasma torpedo Plasma torpedoes are used by the Romulans, Cardassians, and (according to Star Fleet Battles, Klingon Academy and Starfleet Command) the Gorn. The damage of a plasma torpedo spreads out over several ship systems at once, but the torpedo loses