At first glance, it seems a simple matter to calculate the explosive yield of a given quantity of matter and antimatter: E=mc2. However, a bomb with a charge of one ounce of antimatter was described as "(able to) rip away half a planet's atmosphere...equal to 10,000 cobalt bombs" ("Obsession" [TOS]). The former requires a minimum of 1.6*1026 J, far in excess of the 5*1015 J that E=mc2 indicates that one ounce of antimatter (reacting with one ounce of matter) can generate. Furthermore, in "The Immunity Syndrome" [TOS], a semi-liquid (~1 g/cc) energy-consuming space amoeba 11,000 miles long and 2,000-3,000 miles wide was not only destroyed by a torpedo-sized probe containing a simple antimatter charge of approximately 1 kilogram (the Enterprise apparently did not have photon torpedoes at the time), but a million-ton starship inside the amoeba's gelatinous cytoplasm was expelled from the amoeba by the blast as well - which indicated that, at the very least, the gravitational binding energy of the amoeba had been overcome (which would require at least 2.13*1029 J - and more like 3.1*1031 J due to the amoeba's irregular shape and the fact that the charge had to be placed in the amoeba's nucleus, some 10,000 miles from its furthest membrane)! In addition, a crucial plot point of "The Immunity Syndrome" was that the energy released by Starfleet-grade antimatter is of a much different form ("anti-power") than the mechanical and biological energy the amoeba could consume. (Indeed, an antimatter explosion was supposed to be 'indigestible' for an organism that can routinely drain a star of its energy. Furthermore, in the novelization of "Obsession" [TOS], a pound of antimatter was described as able to destroy an entire star system, presumably by inducing a supernova in the system primary.)
One possible explanation is that, prior to its use, the antimatter is fused with a quantity of zero-point energy. This would not only enable relatively small quantities of antimatter to generate vast results, but would explain how antimatter could be "deactivated" ("The Doomsday Machine" [TOS]) or "neutralized" ("Good Shepherd" [VOY]), and why deuterium is preferred as the basis for antimatter in Star Trek over far denser materials such as iron or uranium (lower density = higher volume of ZPE per unit of mass). It would also explain the TNG Tech Manual's assertion that matter-antimatter reactions are about a million times more energetic than fusion reactions, when the difference is actually a hundred times or so - a warp core-mediated matter-antimatter reaction might be far more effective at explosively releasing the fused ZPE energy than a hydrogen-hydrogen fusion. Judging from the energy release of about 1 kilogram of AM in "The Immunity Syndrome" [TOS] and rounding up the magnification to the next two powers of ten (as a compensation for the internal structural strength needed by the amoeba to maintain its tentacled, nonspherical shape despite its unitary composition), this yields an energy efficiency of 9*1032 J/kg - a magnification of ten quadrillion (1016) times, similar to a nadion-based phaser at the "annihilate" setting. (In comparison, the "cobalt bomb" mentioned in "Obsession" [TOS] would have a yield of around 1.22 billion Gigatons - which is comparable to the minimum 100 billion Megaton yield of the thermonuclear warhead employed in the movie Armageddon.)
Note: Although the forced quantum singularity used by most modern Romulan warbirds for their warp drive systems is described as "extremely efficient," in real life, the energy efficiency of dropping matter into a synthetic black hole (specifically, the Shakura-Sunyaev efficiency for accretion onto a Newtonian "black hole") is the square root of the difference between hydrogen fusion and matter-antimatter annihilation. As such, with Star Trek's ZPE-enhanced deuterium, the forced quantum singularity probably achieves an energy efficiency of 9*1029 J/kg. Although this is only a thousandth of what can be generated by an annihilation-powered warp core, the Romulans lacked the technological know-how to design and field annihilation-powered warp cores anywhere near as powerful as those of the Federation or even the Klingon Empire. As such, rather than settle for less powerful combat vessels as the Cardassians, Breen, and Ferengi had done, the Romulans accepted the relative inefficiency of their quantum singularity drives in order to build vessels that were at least as powerful as the peacetime designs fielded by the Federation and the Klingon Empire.
The term "Isoton," a Star Trek unit for the measurement of energy release, has not been precisely defined, but a check of the dictionary reveals that "iso-" is a prefix meaning "equal" ("Isometric" means "of equal measurement"). As a result, it is unlikely to signify some power of ten yet undevised. Instead, it is more likely to represent the 24th century standard of measurement. Since the metric system is also used by Starfleet, I've assumed that the "isoton" is roughly equivalent to the metric ton (just as the metric ton falls between the two imperial measures of "ton.") Because the kilogram is defined as the mass of a certain cylinder of metal kept at the International Bureau of Weights and Measures near Paris, an "isoton" would probably be defined in a way that Federation members can precisely measure without having to travel to or communicate with Earth - perhaps the mass resulting from the conversion of a given quantity of energy (reverse of E=mc2) - a little less than 9*1019 Joules would be sufficient for approximately one metric ton of mass.
As for the isoton as a unit of energy release - in modern-day nuclear weapons, explosive yield is measured in terms of how many tons of TNT the blast would be equal to. Given the wide use of antimatter in the 24th century, the isoton, as a unit of energy release, would likely be used to represent the explosive power of an isoton of matter/antimatter.
Note: Earth's conversion to the use of antimatter as the standard unit of energy release was apparently complete as early as 2152, judging from Malcolm Reed's description of an approximately 2-meter diameter mine as a "quarter of a kiloton" ("Minefield" [ENT]). In terms of TNT, this would be an extremely (to the point of incredulity) low yield for even an obsolete fusion weapon of the size shown. However, if the "kiloton" was instead in terms of real-life antimatter, a much more appropriate energy yield is attained.
Given that Starfleet-grade "refined" antimatter can generate 9*1032 J/kg, this indicates that an isoton could represent the energy release of 1 metric ton of Starfleet-grade M/AM - or 9*1035 Joules. Some support for the scale of this estimate was provided in "The Omega Directive," where Ensign Kim remarked that a 54-isoton explosion was enough to "blow up a small planet." This would require between 1029 and 1034 Joules for non-gas giant planets if the explosion happens at the planet core, with twenty to fifty times more energy needed if the explosion is on the surface or in the atmosphere and at least five orders of magnitude more still if "blow up" refers to the planet's destruction taking place in less than a second rather than over several hours. (A book about the making of TOS has stated that nuclear power compares to the antimatter power systems on Federation starships the same way that a firecracker compares to a thermonuclear bomb.) Furthermore, in "Scorpion Part 2" [VOY], Tuvok stated that a 5 million isoton "multikinetic neutronic mine" would affect an entire star system - an assertion that is in line with how the pre-refit Enterprise was able to effectively blanket the volume of an entire solar system with its phasers in an attempt to hit a cloaked Romulan Bird-of-Prey in "Balance of Terror" [TOS].
Note: By this measurement, the 300-milliliter flask of explosive that Garth of Izar claimed could vaporize an entire Earth-sized planet ("Whom Gods Destroy" [TOS]) would have a rating of at least 0.1 isoton, and almost certainly utilized trilithium and protomatter. In contrast, the "planetkiller" version of the TOS-era starship photon torpedo utilized a penetrating 20-isokilogram warhead to literally reduce an entire Class-M planet to asteroids within a few seconds of the detonation of its impact - and could utterly vaporize the asteroid remains with another such device. ("Operation: Annihilate!" [TOS Novelization])
Although a thermonuclear weapon can theoretically be increased in yield indefinitely, size (and mass) considerations limit the yield of weapons usable by starships. Thus, even as the first pre-warp Earth starships were being designed, efforts were underway to magnify the effectiveness of high-energy warheads.
The proton torpedo was the first of these enhanced warheads. Developed from the "penetrating" thermonuclear warheads employed on "concussion" missiles, pre-warp proton torpedoes used a thermonuclear device as part of a proton-scattering energy warhead (which enhances the blast effect in much the same way as the directed protons boosts the effective KE of a beam, though in this instance the magnification was less than 4 times). Post-warp versions of the proton torpedo were considerably more sophisticated and efficient, utilizing cobalt (and later, di- and tri-cobalt) ZPE-enhanced thermonuclear devices to generate subspace shockwaves of up to 20 petacochranes ("The Voyager Conspiracy" [VOY]) as well as the standard thermokinetic explosion ("Minefield" [ENT]). Eventually, however, the explosive yield of proton torpedoes simply could not compete with its more advanced counterparts (both in terms of raw energy and energy efficiency) and its propulsion capabilities were limited due to its inability to draw reactants from the static (and heavy) warhead. As such, its front-line use is currently limited to pre-warp and minor naval powers (who are generally limited to laser and blaster technology respectively), though plasma- and photon-torpedo-using navies still retain it as an anti-research demolitions device (due to the radioactivity of the target's remains). ("Caretaker" [VOY])
The plasma torpedo was a successor to the proton torpedo, and was developed by the Klingons to address the power limitations of the earlier weapon. Instead of relying on a relatively heavy (and inefficient) thermonuclear warhead to power a proton-scattering warhead, the plasma torpedo uses a magnetic bottle containing a quantity of phased electroplasma (which boosted the electroplasma's kinetic energy effect in much the same way as the phased energy rectification process augments energy weapons). As a result, the plasma torpedo (often colloquially referred to as a photon torpedo for much the same reasons why disruptors are often mislabeled as phasers) was is in effect a missile version of the disruptor bolt, thus precluding the need for the sophisticated magnetic fields required for matter-antimatter warheads. Thus, plasma torpedoes are now commonly used by disruptor-using naval powers (such as the Klingons, Romulans, Cardassians, the Son'a and the Borg).
Note: During the 2260s, the Romulans fielded an independently-developed variant of the plasma torpedo weapon system. According to Graham Kennedy, this version of the plasma torpedo was a simple forcefield generator, that, upon firing, established a force field around itself and a 200-meter diameter concentric field. The launch vessel then established a field bridge through the outer force field and vented its electroplasma system into the space between the two force fields. The breach was then sealed and the torpedo proceeded at high warp speed to its target. Though devastating against fixed fortifications, it was ineffective against starships due to numerous significant drawbacks: it required that the starship practically vent its entire electroplasma system into the field (thus causing an almost total loss of power and precluding its use at warp speeds), the guidance system was severely compromised by the difficulties inherent to operating a sensor system through a high energy plasma field, and any maneuvers undertaken (which were accomplished by venting some of the plasma in a specific direction) came at a significant cost in the yield at detonation. ("Balance of Terror" [TOS]). As such, by the 2340s, the Romulans had abandoned this version of the plasma torpedo for the standard version.
The third - and most powerful - type of enhanced energy warhead is the photon torpedo. This differed from its less sophisticated counterparts by dispensing with the scattering of ions altogether and instead utilizing a ZPE-enhanced matter-antimatter reaction to generate an explosive release of pure energy (photons). The first version of the photon torpedo, fielded no later than 2151 by the Klingons ("Sleeping Dogs" [ENT]), utilized a simple magnetic bottle charged with liquid ZPE-enhanced antideuterium. Although the design's practical maximum antimatter charge of 1 kilogram (to say nothing of the hazards involved in arming and launching the warheads) eventually persuaded the Klingons to abandon the technology in favor of their well-proven plasma torpedoes, Starfleet adopted the weapon in 2153 (as did the Maquis during the organization's 2370-73 lifespan) due to the weapon's power, range, and flexibility ("The Expanse" [ENT]) - and went on to make two major revisions in the photon torpedo's design. The 2215 revision used a more sophisticated matter/antimatter collision device that, upon detonation, fired six frozen deuterium slugs into corresponding magnetic cavities holding antideuterium in suspension. This reduced the detonation time to where it permitted the practical augmenting of the reactants' ZPE charge - for a given mass of reactants, the revised warhead was ten times as powerful as its predecessor. In contrast, the 2271 revision stored both reactants on the torpedo as thousands of minute packets. Following the torpedo's launch, the matter and antimatter packets are mixed in a central combiner tank, though magnetic fields surrounding each packet prevents any contact until the moment of detonation. Due to the greatly increased surface area contact, the current torpedo features a much greater reaction rate than either of its predecessors. Thus, the newer design was not only a full order of magnitude more powerful than the 2215 design for a given mass of reactants, but it could - with a sufficiently powerful launch platform - further overcharge its reactants by up to 8 orders of magnitude. In addition, like the plasma torpedo, the current photon torpedo can augment its flight performance by drawing upon the warhead reactants - but the greater power of the M/AM reactants enables the photon torpedo to make greater adjustments at a lower cost in warhead effectiveness. As a result, Starfleet has continued to use photon torpedoes as its standard missile weapon to this day (though its warships also make use of "enhanced-yield" photon torpedoes).
Just as with energy weapons, the "type" of a torpedo is a logarithmic measurement of the casing's size, used in much the same manner as a ocean-bound torpedo is measured by its diameter. As with energy weapons, Type-1 is the baseline (a 6.2cm long projectile that is small enough to be armed and fired from a human-portable launcher), while each increment is 10 times as large as the one before - a Type-2 casing is 10 times as large as a Type-1, but is one-tenth as large as a Type-3. However, by the mid-23rd Century, Starfleet had phased out the odd-numbered types of torpedo sizes (1, 3, and 5) in favor of exclusively fielding even-numbered sizes for vehicular weapons (the Type-1 torpedo itself has been largely supplanted by specialized personal energy weapons, though it is still maintained in starship armories along with photon grenades and mortars with Type-1 warheads for use by planetside forces). The table below shows the various types of torpedoes fielded by Starfleet and their colloquial names (odd-numbered sizes share the name of the next larger size):
| Type | Length | Mass | Payload | Name | Warheads | Platform | ||
|---|---|---|---|---|---|---|---|---|
| 2 | 13.3cm | 20g | 300mg | Microtorpedo | Photon | Shuttles, Runabouts | ||
| 4 | 52.9cm | 2kg | 30g | Minitorpedo | Ion | Scoutships, Raiders | ||
| 6 | 210cm | 200kg | 3kg | (Standard) Torpedo | Quantum | Starships, Starbases | ||
| 8 | 10m | 20 t | 300kg | Heavy Torpedo | Cruiser-class Warships | |||
| 10 | 46m | 2 kt | 30 t | Superheavy Torpedo | Explorer-class Warships | |||
The introduction of "turbocharging" torpedo tubes in the late 23rd century necessitated a further clarification of the torpedo classification. While its warhead could be "overcharged" with ZPE out of proportion to its size, the degree to which this could be done varied by the platform's energy weapons. As such, the actual warhead yield was represented by a logarithmic measurement. If the torpedo's "class" was identical to the casing's type, then the torpedo's yield was standard in its ZPE/mass charge (9*1034 Joules per kilogram in the current torpedo design) - as was the case when the torpedo was launched without the benefit of a turbocharging torpedo tube (such as Type-6 torpedoes deployed from minor ships like the Danube-class runabout that are too small to carry a full-sized torpedo launcher). However, each class is ten times as powerful as the preceding one - and a Type-6 torpedo can be overcharged to a Class-14 warhead by the torpedo tube(s) of a sufficiently powerful vessel. Furthermore, the modern photon torpedo can also be set to "missile" or "high yield" configurations prior to arming - a photon missile (alternately known as a "photonic missile") reduces the ZPE overcharge capacity of its warhead by a full class in order to triple its acceleration and maneuverability, while a high-yield torpedo diverts power from its propulsion system (reducing its acceleration and maneuverability by two-thirds) to boost its warhead's ZPE overcharge capacity by a full class. As shown by the table below, photon torpedo warhead yield is also related somewhat to the platform's phaser emitter type and quantity:
| Phaser Type | Missile Warhead | Torpedo Warhead | High Yield Warhead | ||||
|---|---|---|---|---|---|---|---|
| < 100 Emitters |
> 100 Emitters |
Class | Yield (Isotons) |
Class | Yield (Isotons) |
Class | Yield (Isotons) |
| non-tube launch | 1 | 0.000002 | 2 | 0.00002 | 3 | 0.0002 | |
| 2 - 6 | 2 - 5 | 2 | 0.00002 | 3 | 0.0002 | 4 | 0.002 |
| 7 | 6 | 3 | 0.0002 | 4 | 0.002 | 5 | 0.02 |
| 8 | 7 | 4 | 0.002 | 5 | 0.02 | 6 | 0.2 |
| 9 | 8 | 5 | 0.02 | 6 | 0.2 | 7 | 2 |
| 10 | 9 | 6 | 0.2 | 7 | 2 | 8 | 20 |
| 11 | 10 | 7 | 2 | 8 | 20 | 9 | 200 |
| 12 | 11 | 8 | 20 | 9 | 200 | 10 | 2000 |
| 12 | 9 | 200 | 10 | 2000 | 11 | 20000 | |
| Phaser Type | Missile Warhead | Torpedo Warhead | High Yield Warhead | ||||
|---|---|---|---|---|---|---|---|
| < 100 Emitters |
> 100 Emitters |
Class | Yield (Isotons) |
Class | Yield (Isotons) |
Class | Yield (Isotons) |
| non-tube launch | 3 | 0.0002 | 4 | 0.002 | 5 | 0.02 | |
| 4 - 6 | 4 - 5 | 4 | 0.002 | 5 | 0.02 | 6 | 0.2 |
| 7 | 6 | 5 | 0.02 | 6 | 0.2 | 7 | 2 |
| 8 | 7 | 6 | 0.2 | 7 | 2 | 8 | 20 |
| 9 | 8 | 7 | 2 | 8 | 20 | 9 | 200 |
| 10 | 9 | 8 | 20 | 9 | 200 | 10 | 2000 |
| 11 | 10 | 9 | 200 | 10 | 2000 | 11 | 20000 |
| 12 | 11 | 10 | 2000 | 11 | 20000 | 12 | 200000 |
| 12 | 11 | 20000 | 12 | 200000 | 13 | 2000000 | |
| Phaser Type | Missile Warhead | Torpedo Warhead | High Yield Warhead | ||||
|---|---|---|---|---|---|---|---|
| < 100 Emitters |
> 100 Emitters |
Class | Yield (Isotons) |
Class | Yield (Isotons) |
Class | Yield (Isotons) |
| non-tube launch | 5 | 0.02 | 6 | 0.2 | 7 | 2 | |
| 6 | 6 | 0.2 | 7 | 2 | 8 | 20 | |
| 7 | 6 | 7 | 2 | 8 | 20 | 9 | 200 |
| 8 | 7 | 8 | 20 | 9 | 200 | 10 | 2000 |
| 9 | 8 | 9 | 200 | 10 | 2000 | 11 | 20000 |
| 10 | 9 | 10 | 2000 | 11 | 20000 | 12 | 200000 |
| 11 | 10 | 11 | 20000 | 12 | 200000 | 13 | 2000000 |
| 12 | 11 | 12 | 200000 | 13 | 2000000 | 14 | 20000000 |
| 12 | 13 | 2000000 | 14 | 20000000 | 15 | 200000000 | |
During the acceptance trials of the variable-yield Mark-6 photon torpedo in 2268, it was determined that its photon warhead had a theoretical maximum explosive yield of 25 isomegatons in its standard-yield configuration. As a result, Starfleet's researchers forecasted a time when the photon torpedo's effectiveness as an anti-ship weapon would be overtaken by the phaser, and efforts were initiated to produce enhanced versions of the photon torpedo that were less limited in explosive yield.
The first enhanced version of the photon torpedo produced was the ion torpedo. Introduced in 2286, this device utilized a standard photon warhead to provide the explosive punch for a proton-scattering warhead in order to greatly magnify its destructive effects (no small feat given the speed and violence of a photon warhead explosion). The first deployed version of the ion torpedo was 40 times as powerful as the latest photon torpedoes of the day, and was first used by the Enterprise-A while in orbit over the planet called Sha-Ka-Ree by the renegade Vulcan Sybok (the restricted effects of such a weapon enabled a full-power ion torpedo to be fired directly into an extremely powerful noncorporeal being without significantly injuring the three Starfleet officers who were only a few meters away from the impact point). An ion torpedo system (along with several dozen torpedoes) was supplied by Admiral Cartwright to General Chang's forces in 2293, where it did much to make General Chang's Bird of Prey a serious threat against the far larger Enterprise-A and the Excelsior. Following the easing of tensions with the Klingon Empire in 2293, the ion torpedo, like the hyperphaser, was gradually retired from Starfleet use due to the increased maintenance requirements of the casings and the improving yields of conventional photon torpedoes. However, with the advent of the Borg threat, the ion torpedo was revived and updated for use on Federation warships. With the improved M/AM detonation rates of current photon torpedoes, modern ion torpedoes are 50 times as powerful as standard photon torpedoes.
The second type of enhanced photon torpedo was the quantum torpedo. Introduced in 2371, the quantum torpedo, like the ion torpedo, is based on the standard photon torpedo, but the newer weapon uses fluoronetic vapor to stabilize a much greater matter-antimatter surface contact than is achievable on a standard photon torpedo. This does boost the yield by 17.8%, but more importantly, it quadruples the M/AM reaction rate, confining its detonation time to 100 nanoseconds, and thus making directing its energy into a zero-point initiator practical - which in turn generates a energy potential 2,500 times that of a standard photon warhead within the zero-point field reaction chamber. Given that the ZPF reaction chamber requires unconventional materials such as dilithium and neutronium in its construction, it is no surprise that it is more difficult to produce than either ion or photon torpedoes, given that some of its crucial components require the use of special industrial replicators (such as those carried on Starfleet Explorers for the purpose of replicating spare warp cores). Due to the increased maintenance requirements (and biohazards) behind systems supporting fluoronetic vapor-using torpedoes, only Federation warships and the Maquis have been known to have used them. In regard to the latter, a shipment of quantum torpedoes was diverted in 2370 by Maquis-sympathizing Starfleet officers to the DMZ, where many were used to arm the captured (and modified) Cardassian Heavy Penetrator codenamed Dreadnought. ("Dreadnought" [VOY])
Note: Given that the Maquis had a remarkable ability to obtain all sorts of Starfleet's technology such as Type-8 phaser banks ("Preemptive Strike" [TNG]) and holocommunicators ("For the Uniform" [DS9]), it stands to reason that Dreadnought's quantum torpedoes were Federation in origin, especially since the Cardassian Union has never used quantum torpedoes as well. As such, I'm inclined to believe that they were among Torres's enhancements to the Heavy Penetrator instead of being the missile's original armament.
One significant benefit of ion and quantum torpedoes is that, to a limited extent, the means by which they boost a photon torpedo's explosive yield also permits the torpedo to be efficiently upscaled for use as a heavy weapon. Previously, the M/AM reaction rate imposed an upper limit of 1kg on ZPE-enhanced AM warheads before the effect per unit of reactant fell off dramatically - a torpedo with 10kg of ZPE-enhanced antideuterium produced significantly less destructive effect than ten standard torpedoes. As a result, maximum photon torpedo size was constrained to Type-6, which resulted in large explorers carrying torpedo casings of the same size as those carried by small scouts. However, due to its proton-scattering warhead, the ion torpedo could be scaled up 4.64 times (for a Type-8 "heavy" torpedo 100 times the volume of a standard sized torpedo) before it experienced a similar dropoff in explosive efficiency. This was even more true for the quantum torpedo - as the M/AM reaction was solely to power the zero-point initiator, and played no significant role in its explosive yield, the quantum torpedo could be scaled up 21.54 times (for a Type-10 "superheavy" torpedo 10,000 times the volume of a standard torpedo) from a standard size prior to a loss in energy potential efficiency of its zero-point initiator. Naturally, the torpedo tubes required for such large torpedoes have to be similarly upscaled - at present, only Prometheus- and Sovereign-class starships are fitted with heavy torpedo tubes, and only the Sovereign-class is fitted with superheavy torpedo tubes. For a scaled visual comparison of standard, heavy, and superheavy torpedoes, click here.
Developed in 2377 as a dedicated Borg-suppression weapon that could be quickly retrofitted to front-line starships, the transphasic photon torpedo employs an omnidirectional array of photon warhead-pumped phasers to generate a multifrequency local release of nadions (as opposed to the straightforward release of photons from an antimatter explosion). Although the inherent inefficiency of the phaser energizing process prevents the transphasic photon warhead from directing more than 1% of its reactants' ZPE charge, the multiple frequencies at which the transphasic warhead simultaneously generates its nadion release renders it significantly difficult (though not impossible) for Borg defenses to adapt to. In theory, this would enable transphasic torpedoes to reliably destroy small Borg vessels (and significantly damage larger ones) with single hits long after more powerful weapons (such as photon and quantum torpedoes) have been adapted to, and thus affords standard starships (and stations) a good chance of stopping a minor Borg incursion on their own - or holding off a major Borg offensive long enough for Starfleet warships to arrive.
However, the transphasic torpedo's Borg-suppression capabilities come at the expense of its operational utility against nonadaptive defensive grids (or adapted Borg defenses), against which it has the performance expected of its low final yield - 1% of that of a standard photon torpedo. Furthermore, the transphasic photon warhead requires unconventional materials such as dilithium, which renders the transphasic torpedo considerably more difficult to manufacture than the standard photon torpedo. Accordingly, the transphasic photon torpedo was intended to compliment, rather than replace, the standard photon torpedoes employed by Starfleet's starships-of-the-line.
Unfortunately, the originally planned 2378 fleet-wide deployment of the transphasic torpedo was unexpectedly postponed for reasons outside of the control of its developers. In a deliberate violation of the Temporal Prime Directive, a 2404 incarnation of Admiral Janeway from a now-alternate timeline journeyed to the USS Voyager in late 2377 in order to equip the starship with transphasic torpedoes and ablative armor generators so that the Admiral's past-self could risk employing the recently-completed Borg interquadrant transwarp hub to return to the Alpha Quadrant sixteen years early. However, in the course of assisting her past-self in getting her ship and crew back to the Alpha Quadrant while simultaneously destroying the interquadrant transwarp hub they were using, the Admiral was assimilated along with her knowledge of the technology behind the transphasic torpedoes, thus rendering the specialized weapon useless in encounters with the Borg for the immediate future. Although the transphasic torpedo's developers are confident that the weapon can be redesigned to recover some of its Borg-suppression effectiveness, they acknowledge to a being that any future users of the transphasic torpedo cannot ever expect those weapons to be anywhere near as effective against the Borg as they were in Voyager's initial use of them.
Note: That transphasic torpedoes primarily owe their effectiveness to their resistance to adaptation rather than being unusually powerful or even technologically advanced has been hinted at through numerous official and canon observations:
- The novelization of "Endgame" [VOY] describes the weapons as "transphasic photon torpedoes," indicating that the weapon was a specialized version of the photon torpedo rather than an entirely new weapon design.
- After "Endgame" [VOY] aired, Rick Sternbach remarked in an on-line Q&A session that, "As to the torpedoes, the Latin root words seem to imply the torpedo or its explosion products do something strange with matter and/or energy, maybe passing through the target matter to disrupt the interior or make the structure otherwise come apart," with no remarks about the weapon's raw power.
- Episodes like "Q Who?" [VOY] and "Scorpion" [VOY] show that, when attacked with unfamiliar weapons technology, Borg vessels are (relatively) easily damaged or destroyed until they adapt (at which point, the Borg vessels attain levels of shielding more typical of vessels of their size). Although Voyager's transphasic torpedoes were able to destroy Borg Cubes with one or two hits prior to the Collective's adaptation to the weapons, the Cubes in "Endgame" [VOY] were small, each only twice Voyager's length on a side (as was typical of Borg Cubes seen in Star Trek: Voyager), and the craters blasted into the Cubes' faces were only an eighth of their edge in diameter. In contrast, the Cube the Enterprise-D disabled in "Q Who?" [TNG] with four Type-10 phaser strikes was a thousand times as large as the Cubes in "Endgame" [VOY], and the craters blasted were a quarter of the Cube's edge in diameter. The two incidents combined suggest that the raw energy yield of Voyager's transphasic torpedoes is about 2 isotons - a hundredth of the yield of that ship's photon torpedoes.
- As with the Doctor's mobile emitter, the fact that the 29th Century Federation time police have allowed Voyager to return with transphasic and ablative armor generator technology to the Federation, despite Admiral Janeway's blatant violation of the Temporal Prime Directive in order to provide her past self with them for basically personal reasons, is a strong indication that what initially appears to be a premature introduction of the technology will not significantly alter the course of history, especially in regards to the balance of power in the Alpha Quadrant. Hence, in Christian R�hl's review of "Endgame" [VOY], Mr. R�hl speculated that transphasic torpedoes were only significantly useful against the adaptive shields of the Borg. That, combined with the Collective's assimilation of the technology in "Endgame," would ensure that writers of future stories would have a clean slate to start from - as befitting Voyager's reputation for being free with "the reset button."