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Torpedo Yields

The Original Series

Just how powerful are the weapons of Star Trek?

A good question, and one without any easy answer. Different sources point to different figures, and the intent of this article is to list the evidence, outline the contradictions, and suggest a solution. Some of the thinking contained within is original to myself, but much is not. I have discussed this subject many times with the residents of various newsgroups and with those of you who contact me via the website over these kinds of issues, and the following could be considered to be a summation of those discussions. There's no way I could begin to remember the names of everybody with whom I have discussed this topic over the last few years, so I will just have to say a general thank you to all those involved who have helped make this article as (hopefully) useful as it is.

In the original Star Trek series there is, surprisingly, a near total lack of any data on how powerful photon torpedoes are. This is because we were only ever given a very vague idea of how destructive these weapons could be.

In 'A Taste of Armageddon', for example, Kirk is captured whilst on the surface of the planet Eminiar VII. Eminiar is fighting a computer-simulated war with its neighbouring planet, Vendikar. When the computers register a person as a casualty they are expected to report to one of numerous disintegration chambers and immolate themselves. Determined to stop the war, Kirk manages to get a message to Scotty in which he orders him to implement General Order 24. Scotty issues the following ultimatum to the Eminian civilisation :

Scotty : "All cities and installations on Eminiar VII have been located, identified and fed into our fire control system. In one hour forty five minutes the entire inhabited surface of your planet will be destroyed."

This is not the only time the Enterprise is claimed to be capable of this level of devastation. In 'Bread and Circuses', Kirk talks to the leader of a world whose civilisation has paralleled that of Earth, but with one important difference : on this world, the Roman Empire never fell. The leader, Marcus, captured a Federation ship's crew some six years earlier and convinced its commanding officer, Captain R.M. Merrick, to work with him. In a conversation with Kirk, Marcus says :

Marcus : "From what I understand, your vessel could lay waste to the entire surface of the world."

Marcus is not himself an expert in Starship capabilities of course, but he has had a ship's captain as his advisor for some six years and so is certain to have a good general idea of the capabilities of the ship.

Both of these examples are phrased somewhat vaguely. Certainly neither could be taken as proof that the Enterprise could 'destroy a planet' in the sense of blasting a whole world into fragments, as the destruction of the Veridian star did to the planets of that system in 'Star Trek : Generations'. Nor could one conclusively assume that the ship could vaporise or melt the entire surface of a planet. But it is certain that at the very minimum the original series Enteprise could eradicate the entire population of a developed world by destroying every significant structure on the surface. Even for a world as 'primitive' as present day Earth this would comprise some thousands of cities and many times that total targets.

We cannot know for sure how much of this kind of massive attack would have been done with phasers as opposed to how much with photon torpedoes. It is conceivable that the phasers would account for the vast majority of the firepower, leaving photon torpedoes as a relatively weak weapon. But this hardly seems credible - if photon torpedoes were really so weak in comparison to phasers then what would be the point in equipping a ship with them? Photons are certainly used to attack other spacecraft on several occasions during the original series, and although it is hard to properly judge the relative effectiveness of the weapons they do seem to be on a par with phasers.

This would indicate that the total yield of the photon torpedo complement of the Enterprise is at least comparable with the entire present day nuclear arsenal of the world, if not considerably greater. To judge individual weapon yields we would have to have an idea of just how many torpedoes the ship could carry, and unfortunately the only reference we have to this is vague indeed - in the aforementioned 'A Taste of Armageddon' Scotty muses that he could treat the Eminians to 'a few dozen photon torpedoes', thus establishing that the ship has at least this many. The upper limit can only be guessed at; the much later, larger and more advanced Enterprise-D carried approximately 250 torpedoes, so it seems unlikely that Kirk's ship would carry significantly more than this.

At the height of the cold war the nuclear powers of the Earth held arsenals with a total yield well into the thousands of megatons. If the Enterprise at least matches this total with only two hundred or so warheads, then each weapon would have a yield well in excess of ten megatons. Weapons with this kind of yield are well within the capabilities of present day science - indeed, bombs with yields of some 50 megatons were successfully tested several decades ago. Producing such energy with a matter/antimatter charge should be relatively straightforward for 23rd century technology. With the recent advent of photons in the tens of megatons range on Enterprise, set a century before Kirk's time, it seems certain that the weapons in use during the original series were at least this powerful. See later on for more details of the Enterprise weapons.

It's worth repeating that this represents virtually the minimum yield that photon torpedoes could have and still fit in with the above episode statements. Higher yields are perfectly possible and indeed quite likely if we are to take phrases such as 'lay waste to the surface of the world' at face value. At least one original series episode points to an even greater level of destruction than this; in 'Whom Gods Destroy', Captain Kirk is trapped in a Federation lunatic asylum which has been taken over by one of its inmates, Garth. The whole planet is covered by a planetary shield, and in the following dialogue the crew consider trying to blast through it :

Scotty : "Mister Sulu. What do your sensors show?"
Sulu : "We can't beam anybody down sir. The forcefield on the planet is in full operation and all forms of transport into the asylum dome are blocked off."
Scotty : "Aye... we could blast our way through the field but only at the risk of destroying the Captain, Mister Spock and any other living thing on Elba II."
McCoy : "How can we be powerful enough to wipe out a planet and still be so helpless!"

Somewhat remarkably, this indicates that the surface of the planet would be totally devastated even by the collateral damage of blasting through the planetary shields! This would would presumably be only a small portion of the total attack, indicating a total firepower much greater than a mere few thousand megatons - perhaps even several orders of magnitude greater. Of course one could suggest that the asylum dome and those living in it are the only living things on the planet. During TOS several planets were shown to be completely uninhabited except for some small installation with as few as two people in it, and thus destroying that one location would indeed be killing every living thing in the world. This would be a rather odd way of phrasing the sentiment, but it is within the bounds of possibility.

Of course we could further suggest that the forcefield was not a 'planetary shield' at all, but merely covered that one facility. Thus we reduce the attack to, potentially, a very small level indeed.

However, this latter point simply doesn't hold up. Consider the discussion on the Enterprise regarding how they might be able to get into the base :

Scotty : "Sensor readings?"
Sulu : "The force field is weakest on the far side of the planet. We can send down a shuttlecraft carrying a team in environmental suits."
McCoy : "It won't work, Scotty. They'd have to cover thousands of miles through poisonous atmosphere before they'd ever reach the asylum."
Scotty : "Aye, you're right. And even if they made it they couldn't carry anything powerful enough to break through the asylum dome."

So, the shield is explicitly stated to cover the entire planet, though the far side is somewhat weaker than the near side - not unreasonable, if it's being generated entirely from the dome rather than from a network of widely spread stations.

And then again, later on :

Scotty : "Well, there's one last thing we might try. Perhaps the ship's phasers can cut through a section of the forcefield at it's weakest point. Where did you say that was located Mister Sulu?"
Sulu : "On the far side of the planet Mister Scott."
McCoy : "Will it leave a margin of safety for the people below?"
Scotty : "Prepare to change orbital path Mister Sulu."

It's perfectly clear in plain simple English - the weakest portion of the forcefield is on the far side of the planet. Thus, the forcefield extends around the planet. And also it's established that a landing party could not carry weapons strong enough to penetrate the asylum dome itself. Bear in mind that in TOS we've seen photon grenades about the size of a baseball which were so powerful that it was worrying to have one go off within a mile of you. The asylum dome must be made of rather strong stuff. And yet blasting through the field, even on the other side of the planet, carried the risk that, through collateral damage only, this facility could be destroyed. Clearly a planetary bombardment by the Enterprise would be a fearsome thing indeed.

Star Trek V

Throughout Star Trek photon torpedoes are used against ships of all kinds, and rarely if ever do they look like they are producing explosions in the tens of megatons range. However, the yield of a weapon being used in this way can be hard to judge; in space the majority of a matter/antimatter explosion would be produced as gamma rays, which are invisible to the naked eye. There would be relatively little in the way of a flash or blastwave as such. Judging effects against ships is fraught with difficulty since Trek ships have shields whose performance characteristics are themselves a matter of debate. Even when torpedoes are used directly against a ship without shields we can tell little; Star Trek vessels are made of fictional materials which are reinforced by a type of forcefield called the 'structural integrity field'. The ability of either one to withstand weapons fire is again a matter of debate, and this is before we consider the fact that an impacting weapon may damage onboard systems and cause secondary explosions which would appear to be part of the weapon yield.

Ideally, then, we would want to look at weapon effects as used against a more conventional environment such as a planetary surface, preferably one in which the target is unlikely to contribute much to the detonation. Fortunately there are several such examples. The first is one of the most interesting, because it implies a yield radically lower than almost any other ever seen. It comes in 'Star Trek V : The Final Frontier'. During the film the Enterprise-A is kidnapped by the Vulcan Sybok, who uses it to travel to the centre of the galaxy in order to reach the fabled planet of Sha'ka'ree. There he and the Enterprise senior staff meet a powerful being who attempts to take over the ship. Kirk orders the Enterprise to fire a photon torpedo at the alien, which it does.

The resulting explosion is anything but megaton level - indeed Kirk, who is hiding behind a rock just thirty or forty feet away, escapes the impact completely unscathed. The yield of the weapon looks to be roughly the equivalent of a small artillery shell.

However, this is not necessarily a problem. When Kirk is ordering the attack he calls the Enterprise and orders the crew to 'listen carefully'. We then cut away to Sybok and the alien being for a while before cutting back to the Enterprise to hear Chekov complain that they will be firing directly on Kirk's position.

So Kirk does not necessarily simply call the ship and order them to fire - the 'listen carefully' line indicates that he is giving orders for something unusual or complicated, and the cuts prevent us from hearing what this might be. Consider that Kirk is hardly likely to order the certain death of his friends and himself - it would be more sensible to simply order the ship to leave, abandoning those on the surface to fight or run from the creature as best they can.

We can only speculate as to what exactly Kirk ordered the Enterprise to do. It's at least possible that he said something like 'listen carefully - I want you to target a photon torpedo on the alien. Disarm the warhead and program it for a simple kinetic energy strike at two hundred metres per second'. This way he is scoring a hit which might kill, disable or at least distract the alien while still giving himself and his friends a chance to survive and escape. We know from Enterprise that even early photon torpedoes could be set so low that they would barely scratch the hull of a shuttle pod, so this kind of thing should be easily within the range of Federation technology.

The Next Generation

As with so many aspects of Star Trek, things began to get more complex with the advent of the next generation. The first indicator of torpedo yields came in the early episode 'Code of Honor'. When the visiting Ligonians kidnap Lieutenant Yar, Picard orders a display of his ship's superior firepower by having some photon torpedoes detonated above the planet. The exact wording is :

Picard : "Set them for a display blast a thousand metres short of the planets surface."

Had he been using 10 megaton warheads on these weapons, this would have represented far more than a 'display blast' - a single such detonation would have laid waste to an area of many hundreds of square kilometres! So it would seem that photon torpedoes in this instance are far, far weaker than they should be. Like the Star Trek V example, there is not necessarily any contradiction here. Picard's use of the words 'display blast' might be taken as an order to modify the torpedo warheads to reduce their yield to a safe level for this situation, which would solve the problem completely.

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You can clearly see the explosion of the torpedo against the surface on the main viewer. [1]

Relatively early in the run of TNG, the Star Trek : The Next Generation Technical Manual (abbreviated to TNG TM) was published. Written by Rick Sternback and Michael Okuda, both of whom created many of the technological aspects of the Next Generation, the book was an in-depth look at the workings of the Galaxy class USS Enterprise-D. It included a section concerning photon torpedoes which stated that they carried a total of 1.5 kilograms of matter and 1.5 kilograms of antimatter in the warhead. Working from Einstein's famous equation of E = mc2, we can calculate the theoretical maximum possible energy which could be released when these masses come together.

 =3 x (3x108)2
 =3 x 9x1016
 =2.7x1017 Joules

A one Megaton explosion releases an energy of approximately 4.3x1015 Joules, so the maximum possible yield of a photon torpedo according to the TNG TM would be 62 Megatons.

The problems begin here because of the concept of canon. The global phenomenon which is Star Trek has spawned countless novels, comic books, posters, interviews, reference guides, cartoons, etc. Unfortunately, many of these contradict one another. To try and clear up the confusion, or at least simplify it a little, the producers declared that in writing future materials that the only materials which should not be contradicted are the filmed episodes and movies; everything else could be safely ignored. This means that the TNG TM figures fall into the non-canon category. That is not to say that we cannot consider them, only that we do not have to take them into account if they become inconvenient. As it happens, I believe that the TNG TM data - and its Deep Space Nine successor - can not only be fitted into an overall picture, but that it makes a vital contribution to that picture.

The next interesting example of a photon torpedo in action comes in the second season episode 'Skin of Evil'. In this episode Deanna Troi is trapped on the surface of a planet when her shuttle is brought down by a being which calls itself Armus. Armus is intent on doing all manner of nasty things to others, and kills Lieutenant Yar when she tries to rescue her trapped shipmate. At the end of the episode Picard manages to talk Armus into such a rage that it is distracted, and the ship beams everybody up safely. Picard then orders the shuttle destroyed and the ship uses a photon torpedo to do this. We see a shot of the torpedo striking the planet on the main viewscreen, resulting in a visible fireball. The planet is suitable to support unprotected Human life and has a gravity equal to Earth's (the creators rarely take the trouble to mention or depict high or low gravity, so virtually all Trek planets have a gravity field identical to Earth's), so should be approximately the same size as our planet. Scaling the blast to the planet gives a diameter for the fireball of approximately 300 kilometres.

Judging the yield of an explosion from the fireball is not a simple matter. Here is what 'The High Energy Weapons Archive' website has to say about it :

'The three categories of immediate effects are: blast, thermal radiation (heat), and prompt ionizing or nuclear radiation. Their relative importance varies with the yield of the bomb. At low yields, all three can be significant sources of injury. With an explosive yield of about 2.5 kt, the three effects are roughly equal. All are capable of inflicting fatal injuries at a range of 1 km.

The equations below provide approximate scaling laws for relating the destructive radius of each effect with yield:
r_thermal =Y0.41 * constant_th
r_blast =Y0.33 * constant_bl
r_radiation =Y0.19 * constant_rad

If Y is in multiples (or fractions) of 2.5 kt, then the result is in km (and all the constants equal one). This is based on thermal radiation just sufficient to cause 3rd degree burns (8 calories/cm^2); a 4.6 psi blast overpressure (and optimum burst height); and a 500 rem radiation dose.

The underlying principles behind these scaling laws are easy to explain. The fraction of a bomb's yield emitted as thermal radiation, blast, and ionizing radiation are essentially constant for all yields, but the way the different forms of energy interact with air and targets vary dramatically.

Air is essentially transparent to thermal radiation. The thermal radiation affects exposed surfaces, producing damage by rapid heating. A bomb that is 100 times larger can produce equal thermal radiation intensities over areas 100 times larger. The area of an (imaginary) sphere centered on the explosion increases with thesquare of the radius. Thus the destructive radius increases with the square root of the yield (this is the familiar inverse square law of electromagnetic radiation). Actually the rate of increase is somewhat less, partly due to the fact that larger bombs emit heat more slowly which reduces the damage produced by each calorie of heat. It is important to note that the area subjected to damage by thermal radiation increases almost linearly with yield.

Blast effect is a volume effect. The blast wave deposits energy in the material it passes through, including air. When the blast wave passes through solid material, the energy left behind causes damage. When it passes through air it simply grows weaker. The more matter the energy travels through, the smaller the effect. The amount of matter increases with the volume of the imaginary sphere centered on the explosion. Blast effects thus scale with the inverse cube law which relates radius to volume.

The intensity of nuclear radiation decreases with the inverse square law like thermal radiation. However nuclear radiation is also strongly absorbed by the air it travels through, which causes the intensity to drop off much more rapidly.'

The fireball would not represent the blast radius of the explosion - it would take the blast some time to propagate outwards over a 150 km radius, but the fireball appeared instantly. Rather, this seems to be the area across which the much more rapid thermal effects would be starting fires. So we are using the first of the equations above. We can ignore the constant since it equals one :
r_thermal =Y0.41
150 =Y0.41
1502.44 =Y

This is in multiples of 2.5 kilotons, so the overall yield would be :
Yield =203020.39 x 2,500
 =507,550,973.27 tons
 =507.55 Megatons

Or about five hundred megatons. This is a more than eight-fold increase over the yield suggested by the TNG TM, and significantly higher than the low end figures generated for the original series, though they are still modest compared to the kind of levels which would be required to truly devastate an entire planetary surface with just a few hundred weapons.

Deep Space Nine

The next interesting use of torpedoes comes in the Deep Space Nine episode 'The Die is Cast'. In this episode a fleet of twenty Romulan and Cardassian vessels have been constructed by the intelligence agencies of those powers. These ships pass through the Bajoran wormhole and proceed under cloak to the Omarian nebula in order to attack the home planet of the Founders. During the run up to the attack the following dialogue takes place between Enabren Tain, Elim Garak, and the Romulan Colonel Lovok :

Tain : "Our plan is to wait until we've entered orbit of the Founder's planet, then decloak and begin massive bombardment."
Lovok : "Computer analysis indicates that the planet's crust will be destroyed within one hour and the mantle within five."

On arrival at the planet the fleet launches a bombardment lasting some few seconds. We see the impacts of the weapons on the surface, resulting in shock waves which travel over a significant section of the planet's surface. The following dialogue accompanies the attack :

Tain : "So much for the Dominion. Open fire!"
Woman : "The first barrage is complete."
Tain : "Effect?"
Woman : "Thirty percent of the planetary crust destroyed in opening volley. No change in life form readings."
Tain : "What? That's impossible. Some of them had to be killed!"
Woman : "Our sensor readings have been confirmed by three other warbirds. There's no change in the number of life signs on the surface!"
Garak : "They're using an automated transponder to send back false sensor readings. The planet's deserted!"

inline image
This shot shows multiple weapons being fired in the opening bombardment. [2]

inline image
As the weapons strike we see the initial fireball and the blast wave expanding outwards at tremendously high speed. [2]

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This view shows the blast waves continuing to spread over the surface of the planet. [2]

It soon transpires that Colonel Lovok is a changeling infiltrator placed within the Romulan intelligence service in order to encourage this attack so that the fleet could be led into an ambush; moments after the above dialogue a force of 150 Jem'Hadar ships emerged from the nebula and attacked.

It has been claimed by some that the damage projections made by Lovok were a lie and that the damage done to the planet was an illusion generated by the Founders. However, these claims make little sense. There seems to be no reason for Lovok to tell such a lie - it doesn't gain the Founders anything to have Tain and Garak think that the attack will be ten or a hundred times faster than it really would or could be. And even a basic knowledge of military technology on the part of Tain or Garak would have been enough to allow them to see through such a lie, putting the Founder's whole plot at risk. Simulating planetary scale damage would also be a difficult and pointless business. Immense fireball explosions and atmospheric shock waves are clearly visible on the surface of the planet; simulating these would involve holographic projections covering hundreds of millions of square kilometres! And what would it accomplish? The fleet was already in the Founder's trap at this point, the Jem'Hadar were moments away from launching their attack, so making Tain and co. think that their attack was succeeding is pointless.

So it seems beyond reasonable doubt that both the damage projection and the attack were genuine. Given this, we can work up a few figures concerning the yield of the weapons used.

We can only make guesses about the relative sizes of the crust and mantle, the materials within them and the damage expected to be inflicted upon them. As usual for Star Trek the Founder's planet has a Human-habitable surface and identical gravity to Earth's, and so is likely to be approximately the same size and density as Earth.

On Earth, the crust has a surface area of about 510 million square kilometres. Its thickness ranges from about 5 kilometres under the ocean to about 70 kilometres in the continents; since there is about three times as much ocean as continent, the average thickness would be about 21 kilometres. So we're looking at over ten billion cubic kilometres of rock massing about 2.9x1022 kg. The Earth's mantle is about one hundred times the volume of the crust and is somewhat denser; it is 3,000 kilometres thick, with a volume of over nine hundred billion cubic kilometres and a mass in excess of 4.25x1024 kg.

To give an idea of the range of possibilities, I am going to present 'high end' and 'low end' cases. In the 'high end' I will make assumptions that tend to lead towards torpedoes with the maximum yield consistent with this episode. In the 'low end' I will make assumptions that tend to lead towards torpedoes with the lowest yield consistent with the episode.

First, the 'high end'. Here I will use Lovok's damage predictions of the whole crust and mantle being destroyed during the attack. I will assume that by 'destroyed' he meant 'vaporised'.

In vaporising any substance, you have to heat it up to its melting point, then give it sufficient energy to turn it from a solid to a liquid, then heat it up to its boiling point, then give it sufficient energy to turn it from a liquid to a gas. The mantle of a planet is typically close to its boiling point anyway and since the mantle is far larger than the crust, I am going to concentrate solely on the last stage. It's hard to find out just how much energy it takes to turn a given mass of rock from liquid to gas, but for comparison it's about twenty thousand Joules per kilogram for Helium or about five million Joules per kilogram for Copper.

Vaporising the mantle would therefore take on the order of 1030 Joules - an attack equivalent to 1014 Megatons. This would be the weapon output of the entire fleet throughout the whole attack, from both beam weapons and torpedoes. In line with my aim to make the yield of the weapons as high as possible in this example, I will assume that the torpedoes were expected to contribute the entire energy of the attack. We know that the Galaxy class Starship carries approximately 250 torpedoes, so assuming that the Cardassian and Romulan ships have comparable arsenals the whole fleet would carry 5,000 weapons. So each of these weapons would have a yield of 20 billion Megatons.

So much for the upper case, what about the lower end? Looking at the actual attack itself, it was reported that thirty percent of the crust was destroyed in the opening volley. This time we are after the lowest weapon yields possible, so we will minimise the damage by assuming that 'destroyed' does not mean 'vaporised' as before, and that in fact the attack did not even shatter the crust into pieces. Rather, let's see what numbers we arrive at if we just look at an attack which simply damaged one third of the surface of the planet.

Again taking the planet to be roughly Earth-sized, the damage would cover 170 million square kilometres. To further reduce the yield of our torpedoes I'm going to assume that 90% of this was done by the beam weapons, with only 17 million square kilometres affected by torpedoes. And to cut the numbers down even more I'm going to assume that the damage inflicted was of the most feeble kind. According to the High Energy Weapons Archive quoted above, for any given weapon yield the most widespread effect is thermal - meaning any nuclear bomb will start fires at far greater distances than it will knock down buildings. So for my low end estimate I am going to say that the 17 million square kilometre area was only affected to the extent of having fires started on it.

The fleet launches only ten torpedoes to cause this damage, so each one accounts for 1.7 million square kilometres. This means that each torpedo has lit fires over an area of about 735 kilometres radius. Using the above equations we can get an idea of the yield required to do this damage :

r_thermal =Y0.41
735 =Y0.41
7352.44 =Y

This is in multiples of 2.5 kilotons, so the overall yield would be :

Yield =9,793,653.38 x 2,500
 =24,484,133,461.48 tons
 =24,484.13 Megatons

Giving each torpedo a yield of 'only' 24 thousand megatons.

It is worth reiterating that this represents virtually the lowest possible yield of the weapons used in the attack; the attack was described as 'destroying' thirty percent of the planet's crust, but to generate this figure we are assuming that the torpedoes only contributed 10% of this, and that rather than 'destroy' the crust all the torpedo attack did was light fires over the affected area! Yet even with this exceptionally weak interpretation of what was seen, the yield of each weapon is well into the tens of thousands of megatons.

So we can reasonably expect that the weapons used in 'The Die Is Cast' have yields somewhere between about 25 thousand and 20 billion Megatons. The 'real' figure will depend on where you pitch your assumptions between the two extremes I have used here; for example if you took ten torpedoes as doing one half of the damage in the actual attack, via blast rather than thermal effects, then each weapon would have a yield of about 14 million Megatons. Even then there are some factors I have neglected in this analysis - for example all of these figures assume that the entire energy of every weapon is expended in a useful (i.e. destructive) manner, whereas in fact some of it would be radiated away into space. This alone would increase the yields here significantly.

Deep Space Nine Technical Manual

Like the TNG TM, the Deep Space Nine Technical Manual is a non-canon book and we do not need to take it into account should it become inconvenient to do so. This book is also notorious amongst tech-minded Star Trek fans for its high level of inaccuracy. However, it can be accommodated within the scheme I have in mind so we will review some of the data in it regarding torpedo yields.

The following quote from page 84 deals with photon torpedo yields :

'The basic external configuration of the photon torpedo carried onboard Deep Space 9 and its attached starships has changed little from 2271 to 2375. The body is an elongated elliptical tube fabricated from molded gamma-expanded duranium and a plasma-bonded tritanium outer skin. The current casing measures 2.1 by 0.76 by 0.45 meters and masses 186.7 kilograms dry weight, slightly less than the previous design. Penetrations by phaser cutter are still provided for warhead reactant loading, hardline ODN connections, and propulsion-system exhaust grills. The standard internal components include deuterium and antideuterium supply tanks, central combiner tank, and their respective magnetic suspension components; target acquisition, guidance, and detonation assemblies; and warp sustainer engine. The hafnium-titanide supply and combiner tank shells have an increased capacity of 5 percent, resulting in a slightly higher explosive yield, now rated at 18.5 isotons. Reduced optronics component complexity had driven the tankage increase.'

This quote from page 85 refers to the initial development of a prototype quantum torpedo :

'During the upgrade testing of the Mark-IX warhead, it was determined that the theoretical maximum explosive yield of 25 isotons had finally been reached for a matter-antimatter reaction. Existing and future threat force conflicts drove the development of a new defensive stand-off weapon that could be deployed on specially equipped starships, starbases, and planetary-surface fortifications. Advances in rapid energy extraction from the space-time domain known as the zero-point vacuum eventually led the starfleet R&D facility on Groombridge 273-2A to test a prototype continuum-twist device with a calculated potential of 52.3 isotons.'

Later in the same page, this quote refers to the production model quantum torpedo :
'The zero-point initiator is powered by the detonation of an uprated photon torpedo warhead with a yield of 21.8 isotons, achieved through increased matter-antimatter surface area contact and introduction of fluoronetic vapor. The MIA reaction occurs at four times the rate of a standard warhead. The detonation energy is channeled through the initiator within 10-7 seconds and energizes the emitter, which imparts a tension force upon the vacuum domain. As the vacuum membrane expands, over a period of 10-4 seconds, an energy potential equivalent to at least fifty isotons is created. This energy is held by the chamber for 10-8 seconds and is then released by the controlled failure of the chamber wall.'

The first quote refers to the yield of a photon torpedo in terms of 'isotons' a term which is used with increasing frequency throughout the last decade or so of Star Trek production. There is nothing in the Tech Manual and little in the shows themselves to indicate exactly what an isoton is, but I will make some suggestions later.

One thing we can do from the quotes in the TNG and DS9 tech manuals is come up with a conversion factor between isotons and Megatons. If we take the 'theoretical maximum' of 25 isotons referred to in the second DS9 TM quote and assume that this is the same as the 62 Megaton theoretical maximum yield calculated form the TNG TM earlier, the this would mean that each isoton is the equivalent of 2.48 Megatons. Using this conversion ratio we can generate Megaton yield figures for any warhead which is given a figure in isotons and vice versa.

We can also calculate an efficiency for the detonation of a photon torpedo; the first of these three quotes refers to an actual yield of 18.5 isotons, while the second refers to a theoretical maximum yield of 25 isotons, so the efficiency would be 18.5/25, or 74% exactly. This would mean that the standard photon torpedo would have a yield of 45.88 Megatons out of the theoretical maximum of 62 Megatons.

As something of a side note, the yield of a quantum torpedo is more difficult to determine than most. The third DS9 TM quote indicates that the weapon uses a 21.8 isoton matter/antimatter warhead to initiate cause a 50 isoton zero point explosion. This is presumably analogous to the way that a present day thermonuclear bomb uses a fission explosion to initiate a much larger fusion reaction. However, it is unclear if some portion of the matter/antimatter detonation is 'used up' in creating the conditions necessary for the larger blast. As a result the yield of a quantum warhead could be anywhere between 50 and 71.8 isotons, equating to between 124 and 178 Megatons. This would mean that the quantum torpedo warhead is not actually all that powerful; certainly it has nowhere near the power of the large surface attack warheads used in 'Skin of Evil' and 'The Die is Cast'. See the conclusion section for further discussion of this.


Voyager used isoton yield figures several times, unfortunately not in a terribly consistent manner. The first came in 'Scorpion, Part II'. In this episode Janeway made an alliance with the Borg against a deadly alien race which the Borg dubbed Species 8472. Janeway agrees to work with Seven of Nine, a Borg drone, to modify Voyager's weapons so as to fight their common enemy. Seven of Nine suggests that they work on a Borg weapon and brings up a diagram :

Tuvok : "A multikinetic neutronic mine. Five million isoton yield. This would affect an entire star system."
Seven : "Correct."

Janeway declines to create a weapon of mass destruction and suggests they work on Voyager's torpedoes instead. Seven activates another display :

Seven : "Voyager's weapons inventory. Photon torpedo complement thirty two, class-six warheads. Explosive yield two hundred isotons."

A five million isoton yield would equate to 12,400,000 Megatons, which is certainly an impressive blast. Voyager's two hundred isoton warheads equates to 496 Megatons. Clearly, then, Voyager's warheads are far more powerful than the standard 18.5 isoton model referred to in the DS9 TM. Amazingly, 200 isotons is almost exactly the same yield as was calculated for the 'Skin of Evil' weapon - so it's entirely possible that Picard used a warhead of this type to destroy the shuttlecraft. It remains far short of the weapons used in 'The Die is Cast', though.

The episode 'Dreadnought' suggests that Voyager's torpedoes are somehow different or more powerful than standard models. Here the ship is facing a Cardassian weapon which was captured by the Maquis and reprogrammed by B'Elanna Torres, now Voyager's chief engineer. Dragged to the Delta Quadrant the same way Voyager was, it wandered for some time before accidentally locking onto an innocent planet. The weapon is equipped with powerful defensive systems, and the crew are gloomy about their chances of defeating it. Janeway declares that the ship's torpedoes are 'type six', a model introduced after Torres reprogrammed Dreadnought, and that as a result 'they just might get through'. Yet it doesn't seem like the Type VI has more overall power than previous torpedoes; as mentioned, the weapon used in 'Skin of Evil' had an almost identical yield. I will go into more detail on this in the conclusion below.

The Dreadnought itself is said to be equipped with a warhead comprising one thousand kilograms of antimatter and another one thousand kilograms of matter. The theoretical maximum yield from this warhead would be 1.8x1020 Joules, or 41,860 Megatons.

The confusion begins in the episode 'Living Witness'. Here we encounter the after-effects of an encounter Voyager had with two Delta Quadrant species, seven hundred years after the ship passed through. A museum exhibit of Voyager artifacts includes a photon torpedo casing, and the museum guide describes it as follows :

Guide : "I wouldn't touch that if I were you. One of the Voyager's torpedoes - twenty five isoton yield. It could destroy an entire city within seconds. It's been inactive for centuries but you never know."

Fortunately this one is fairly easy to discard. The whole thrust of the episode is that the Kyrian information on Voyager is woefully inaccurate - for instance they consider the Starship's armament to include a triple-armoured hull, thirty torpedo tubes, and twenty five phaser banks. They believed that the EMH was a robot, that the crew included a complement of full Borg-type drones, that torture and murder were common Federation tactics. It's not hard to believe that they made a mistake regarding the warhead yield.

The next mention of isoton yields comes in 'The Omega Directive'. In this episode the Voyager crew is on a mission to destroy a dangerous molecule which have the potential to destroy any chance of warp drive over a large part of the galaxy. They choose to use a 'gravitic warhead', which Tuvok and Kim install into a standardphoton torpedo casing. The following dialogue ensues :

Kim : "This looks like enough for a 50 isoton explosion."
Tuvok : "Fifty four, to be exact."
Kim : "What are we planning to do, blow up a small planet?"
Tuvok : "I don't know."
Kim : "This warhead isn't standard issue. Who designed it? The captain?"
Janeway : "Mr. Kim, you ask too many questions. Change of plans, gentlemen. Increase the charge to 80 isotons."
Tuvok : "Aye captain."
Janeway : "Harry, when you're done here give B'Elanna a hand with the shuttlecraft. She's reinforcing the hull."

This would put the standard gravitic warhead at 133.92 Megatons and the uprated gravitic warhead at 198.4 Megatons, both of which are considerably more than the standard photon but still considerably short of the 200 isoton model which Voyager carries, let alone the much larger surface attack models. Kim's line about blowing up small planets seems to be something of an exaggeration, although it's conceivable that gravitic warheads are able to do more damage with less yield than matter/antimatter weapons.

One has to wonder why the crew is going to the trouble of making an 80 isoton weapon when their standard photons are far more powerful than this. Again, it's possible that gravitic warheads are an effective method of destroying the Omega molecules whilst matter/antimatter explosions are not.

If we ignored the Borg claim that Voyager's standard warheads have 200 isoton yield, then Voyager has actually been quite consistent in its use of this yield. Then again, the evidence contradicting that figure is somewhat patchy, either coming from questionable sources or concerning weapons which may be quite different in their operation and effects from matter/antimatter warheads. For more on how the figures can be reconciled see the conclusion below.


The episode "The Expanse" features the NX class Enterprise receiving various upgrades, including "photonic torpedoes". These are externally very similar to the standard photon torpedo casing we have seen since Star Trek II - differences are confined to colour, markings and the like. Reed and Trip discussing the weapons as they are loaded aboard :

Reed : "Photonic torpedoes. Their range is over fifty times greater than our conventional torpedoes. And they have a variable yield. They can knock the comm array off a shuttle pod without scratching the hull, or they can put a three kilometre crater into an asteroid."

This confirms two important facts - firstly, the yield of the weapons. It's hard to find a way of calculating the size of the crater a particular weapon yield will create, especially as not all asteroids are alike. For comparison, however, the USA's largest ever thermonuclear weapon test (the Bravo test on the Bikini atoll) yielded 15 Megatons, and created a crater 1.8 kilometres in diameter and 73 metres deep - see this external link for details. So the Enterprise photon torpedoes must have a yield comfortably larger than this. In fact it's quite possible that the yield of these weapons exceeds the 45 Megaton yield of the standard photon torpedo calculated from the TNG and DS9 technical manuals, which could be seen as suggesting higher yields for the warhead of the TNG era.

Secondly, this is another datapoint concerning the variable yield of a photon warhead, and confirming that they can be set to have a very low effect indeed. A blast which can "knock the comm array off a shuttle pod without scratching the hull" is precisely the kind of thing that Kirk may have ordered the Enterprise-A to fire against "God" in Star Trek V.

What's an Isoton?

I've already talked much about isotons above, and have shown that we can come up with a conversion ratio of one isoton being equal to 2.48 Megatons. As far as this article is concerned, that is sufficient for my purposes. But I'm going to suggest an explanation for what exactly an isoton is in the context of Star Trek.

Prefixes like 'kilo-' and 'Mega-' are simple multipliers, meaning 'one thousand' and 'one million' respectively. From the above ratio it may seem that 'iso-' is simply a multiplier that means 'two point four eight million'. Unfortunately, things are not so simple.

The prefix 'ISO' is widely used in Voyager (many say too widely). In 'Equinox, Part I' Chakotay suggests that they should recover the dilithium crystals from the Equinox and Gilmore replies 'What we have left of them. I'm afraid we only have a few isograms.' Later in the same episode Janeway talks about recovering 'ten isograms' of a particular compound from the body of an alien being. This makes it hard to believe than 'ISO' is a simple prefix like 'Mega-', and harder still to believe the above ratio. If the Equinox had even one isogram of dilithium left in its engines this would amount to nearly two and a half metric tons of the stuff, while Ransom would have extracted twenty five metric tons of his compound from an alien that was only two feet long!

I prefer to think of 'ISO' as representing a new measuring system. Throughout Human history we have periodically refined our definition of the units we use in order to simplify our measuring systems. So we have the metric ton (or tonne) of 1,000 kg and the older version of 2,240 lb. (just over 1,016 kg). My guess is that some time in the future the Federation came up with a new set of definitions. One could speculate that the body which decided this was called the 'Interplanetary Standards Organisation', and so the gram became the ISO gram, the second the ISO second, etc. This would mean that when a Federation character talks of grams he or she always actually means 'isograms'. The ISO would only be missed out of laziness, in much the same way that a person today might say 'tons' rather than 'metric tons', or 'gallons' rather than 'US gallons' or 'UK gallons'.

Most of the time when we redefine units we change them only very slightly, if at all. This avoids confusing people as to how much of something they are buying or using. In all probability, then, an isoton weighs almost exactly the same as a present day ton.

All very well, but what does it then mean to say that a torpedo has a warhead rated at 18.5 isotons? It doesn't seem likely that the warhead actually weighs that much material, and certainly this would contradict the TNG TM claim of a 3 kg matter/antimatter charge in the standard photon torpedo.

Again, I would suggest that this meaning would parallel present day terminology. When we talk of a 'one Megaton bomb', we do not literally mean that the bomb weighs one million tons. Rather we mean that the device has an explosion as devastating as one million tons of conventional explosives. Or at least, that was the initial meaning of the word 'Megaton' - rather ironically considering the subject under discussion, the definition of a 'Megaton' was changed to mean the release of a specific amount of energy.

I would suggest that when applied to warhead yields, isoton is used in the same way - the warhead is being described as possessing as much explosive power as one ISO ton of some 24th century explosive. What this explosive is isn't really important, though it would need to be extremely powerful for a single ton of it to be the equal of a good sized nuclear explosion.

So there you have it - an isoton is just a futuristic version of a regular everyday ton when used for weights, and is a futuristic version of a Megaton when used for weapon yields.


We have identified the following weapons or possible weapons :

Standard Photon18.545.88Isoton yield of a standard photon stated in the TNG TM; megatonnage determined from DS9 and TNG TMs.
Standard gravitic54133.92Isoton yield stated in 'The Omega Directive'.
Quantum50 - 71.8124 - 178Isoton yield stated in the DS9 technical manual
Uprated Gravitic80198.4Isoton yield stated in 'The Omega Directive'
Type VI photon200496Isoton yield stated in 'Scorpion'
Surface attack weapon,
204.65507.55Megaton yield calculated from the explosion seen in 'Skin of Evil'. This may be an older version of the warhead used on the Type VI.
Surface attack weapon,
9,87224,484This is the low end yield of the weapons used in 'The Die is Cast', and assumes a small torpedo attack which starts fires across some 3% of the surface of a planet.
Dreadnought16,87941,860Theoretical maximum yield from a 2,000 kg matter/antimatter charge.
Multikinetic neutronic mine5,000,00012,400,000Borg weapon, yield stated in isotons in 'Scorpion, Part II'
Surface attack weapon,
8,000,000,00020,000,000,000This is the high end yield of the weapons used in 'The Die is Cast', and assumes a pure torpedo attack which vaporises the entire crust and mantle of an Earth sized planet.

There seems to be a clear disparity in the yield of 'standard' photon warheads with yields in the tens of megatons and those used against the surface of planets which are at least thousands of times larger. I propose that Star Trek weapons fall into one of two categories, 'anti ship' and 'surface attack'. Think of the former as being analogous to today's air to air missiles - small, light, fast and highly agile but armed with light warheads which are intended for use against the relatively light shielding of a Starship.

The latter would be more like today's heavy ground attack bombs - much larger, much heavier, not nearly fast or manoeuvrable enough to attack a Starship but packing a very powerful punch for use against large, stationary and/or heavily defended targets such as ground bases or space stations. Such weapons may be standard photon casings with extra warhead material attached - in 'For the Uniform' Captain Sisko attached a cargo pod to a quantum torpedo in order to spread contaminants through the atmosphere of a planet. Or they may be 'stretched' versions of standard weapons with extra internal volume for larger warheads. Or they may represent something wholly different from a standard torpedo; imagine a huge tank of antimatter with an inertial guidance system and just enough engine attached to get it out of orbit.

One problem to explain is the idea that Voyager's Type VI photon torpedoes, which are used almost exclusively against spacecraft, fit more into the surface attack category. There are two approaches to take to this :

First, assume that the Borg got it wrong. Voyager's torpedoes are not in fact 200 isotons, but rather the 25 isotons that the Kyrians claimed in 'Living Witness'. This puts the Type VI firmly into the upper end of the 'anti ship' photon range. Janeway would have some grounds for believing that the weapon would be effective against Dreadnought, since it is still about 35% more powerful than the standard 18.5 isoton weapon referred to in the DS9 technical manual. Under this scenario the quantum torpedo represents a significant increase in anti-ship firepower, at least twice as strong as a Type VI; the graviton warhead has an even higher yield still. The surface attack weapons seen in 'Skin of Evil' and 'The Die is Cast' remain much heavier than normal warheads.

Second, assume that the Borg were correct and the Kyrians mistaken. The Mark VI then becomes a sort of compromise between the anti ship and surface attack warheads; a much larger warhead than most anti ship weapons, but not very powerful by the standards of surface attack warheads. It is like a large air to air missile that has a secondary role against surface targets. There is a good analogy to this in the real world; the US Sea Sparrow is a fairly large anti aircraft missile, some models of which can also be used against surface targets. Voyager would be an ideal choice for this kind of weapon because on a small ship like the Intrepid class where space was at a premium, it would make sense to carry a multipurpose weapon rather than one set of anti-ship photons and one set of surface attack photons. In this scenario Janeway has more reason to believe that the Type VI would be effective against Dreadnought, since it is now one of the more powerful anti ship weapons around. The difference between Janeway's Type VI and Picard's 'Skin of Evil' weapon is uncertain; perhaps Picard's weapon was a pure surface attack model which could not have been used against a spacecraft like Dreadnought at all, or perhaps Janeway's Type VI is more effective because it focuses the blast in a manner akin to a shape charge, or adapts itself to shield frequencies, or has some other advantage other than raw explosive force.

Under this second case the quantum torpedo is no longer the super-weapon that many fans consider it to be; more powerful than the standard photon, it lags far behind the Type VI in raw yield. This is not actually a contradiction with the show. Canon details of the quantum torpedo are extremely scarce - we have never even heard it stated on screen that the quantum torpedo has a higher yield than standard photons. Again, the advantages of this weapon may lie elsewhere than raw explosive power.

Both of these explanations fit the facts, but I tend to favour the second one. Given the level of accuracy the Kyrians demonstrated regarding Voyager, they seem to me to be far more likely to be the ones making the mistake about the torpedo yield. My instinct is that the Type VI a compromise weapon, a warhead just big enough to be useful against planetary surfaces, just small enough to be useful against enemy ships. Indeed, I think it likely that the Type VI represents a modification of the exact same design Picard used in 'Skin of Evil', perhaps with engine and guidance systems altered to allow the anti ship role.

Another question is whether we need to incorporate the Technical Manuals at all. Since we have a canonical indication of a 30+ Megaton yield for the photon torpedoes of Enterprise, 45 Megatons for the TNG era seems low - and the only source for this number is the non-canon tech manual. If we disregarded this, and took the "Skin of Evil" 500 Megaton torpedo as a standard yield for a TNG torpedo, things would be somewhat simplified. We would, however, lose the non-canon yield figures for the Quantum torpedoes from the DS9 TM. For the moment I tend to favour keeping the TMs in, and have written this article with this in mind.

Given that we are assuming warhead yields for even anti ship weapons in the tens of megatons, it's worth mentioning again that this does not often seem to be the case when the weapons are used against spacecraft. But this is not necessarily a contradiction; the effectiveness of shielding, structural integrity fields and hull materials are almost arbitrary and this makes it very hard to say that a torpedo must have such and such a yield because it blasted away a certain section of hull.

Colour key

Canon source Backstage source Novel source DITL speculation


# Series Season Source Comment
1 TNG 1 Skin of Evil
2 DS9 3 The Die is Cast
Series : TNG Season 1
Episode : Skin of Evil
Series : DS9 Season 3
Episode : The Die is Cast

© Graham & Ian Kennedy Page views : 91,511 Last updated : 16 Jan 2021