Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

One of the Horus Heresy books talks about marines fighting underwater

Missiles are easy enough if you don't mind a teensy tiny bit of handwaving - torpedoes are similar enough in shape that you could probably just arbitarily declare all of your missile launchers are man-packed torpedo launchers (the troops knew that they were going to be fighting underwater, so they swapped them out at the armory beforehand). "Frag torpedoes" would probably depend more on the concussive blast than the fragmentation for damage. I'm not sure how Krak warheads would work underwater, though.

Eldar plasma torpedo... *ouch*

Many assault rifles will function underwater. The AK47 and all of its descendents are, as such things go, true workhorses, and will continue to operate in the absolute worst battlefield conditions. Any assault rifle firing caseless ammunition will also continue to function, at least for the first clip, as such weapons are watertight, and a bullet in the chamber prevents water from getting to the propellant block.

Hell, the same is true of some muzzle-loader weapons. Rifles recovered from creeks and rivers near battlefields of the American Civil War were found to be still-serviceable, with the ball and wadding forming a seal at one end, and the cap-and-hammer a seal on the other, which kept the powder between the ball and the nipple-cap dry... for 150+ years!

ZZApp gun underwater

Anyone old enough to have played the original Quake remember what happends when you fire a lighting staff underwater


Frag missiles could be rerigged as micro-torps or bundles of aquadynamic shards (like drill bits with fins) that burst in all directions from a central core projectile.

Krak warheads would work just fine, as they are basically an armour piercing sabot containing a shaped charge that expodes on contact. (presumably.. there's not a lot of detail out there). A modern torpedo's warhead works the same way.

I want to see a necron vs astartes fight on the sea bottom sometime, with assault marines having impeller packs instead of jetpacks, and streamlined speeders

As has been noted previously, most weapons would work underwater, however they mostly rely on a discharge of energy at the user's end to casue damage ad the target end. In most cases the effects of the water will be to dissipate the energy local to the user, either pulping them with shockwaves or flash-boiling them with dissipated heat.

Caseless weapons would likely suffer from the same problem as normal slug-throwers as the water will get down the barrel and help propagate the shockwave from the propellant ignition. The propellant for all modern ammunition is self-oxidizing and hence doesn't need air to burn.

Flamer fuel is often described as self-igniting on contact with oxygen (so why GW insists on adding pilot lights I don't know) so unmodified kit may or may not work underwater. You could, however, add an oxidizer to help it burn. However the range would likely be extremely limited due to the problems of pushing liquid through other liquid (also if its petroleum based the fuel would float anyway). White Phosphorous based weapons, however...

TrollPie wrote:Since lasguns are effectively beams of light, the refraction would make any aiming pretty much useless.

This is incorrect on two accounts... Firstly refraction would only occur if the laser were fired into the water from outside (or vice versa), Fired from under the water through the water, there would be no refraction.

Secondly: Even if the laser was being fired into the water from outside, aiming it would be completely natural and intuitive because the light illuminating the target would be refracted at exactly the same angle as the laser. All you would have to do is aim where you where looking and physics would take care of the rest.

Unlike an arrow, which would appear to bend when entering the water (but in fact remain straight). A laser will appear straight (because it really does bend).

You're not taking water density into account based on temperature variation.

The whole point about diffraction of light is that it is the light wave being bent by transitioning between substances of different density.

A laser beam is a beam of light. If you can see the target, you point straight at it and the beam will hit it. You could shoot a laser down a tunnel filled with mirrors and hit a target you could see. The beam would just bounce off the mirrors the same way the light from the target bounced its way up to you so you could see it.

In practical terms, a lasgun is a completely sealed weapon with no moving parts. It would have none of the problems of a projectile weapon underwater. The main problem is that IRL water like the sea, there is a lot of suspended particulate matter which will absorb the beam and reduce power and range.

Melta and Plasma weapons -- As mentioned above, there is the danger of the shot producing an immediate steam explosion.

Flamethrower -- The fuel needs oxygen to burn, so it wouldn't work.

Projectile weapons generally -- Might or might not work. It depends on their method of operation. The bullet will create a serious pressure in the barrel when fired against a column of water. This might damage the breech mechanism. Gas operated weapons would have a similar problem of getting enough gas pressure against the water pressure to work the action.

Shayden wrote:

MikZor wrote:

Shayden wrote:A laser is a beam of light, light travels slightly slower in water. the only problem is the color of the laser. From the games, it is shown as red, which is the first color to disappear deep underwater. If they need range, a shorter wavelength would do the trick.

A plasmagun fires a (surprise!) a ball of plasma. I honestly don't know what would happen here, but the water may be advantageous when it comes to heat management. Thats all I can say on that.

The meltagun is very similar to a plasmagun, the main difference being the meltagun fires a column of plasma instead of a ball of it. It achieves this by agitating the air to a very high energy state, and it results in a column of plasma. Again, I don't know what would happen.

Can the wave length of lasguns be changed? I know certain pattern lasguns have alternate settings, so would the high setting shorten the wavelengths?

My thoughts about plasma are that the water would cool the gun alot better so it wouldn't overheat as often and that the plasma is contained within the magnetic field until it's disrupted, but does it give off it's heat while its in the magnetic field? Thus still having the same heat problems as the lasgun.

Melta doesn't have a magnetic field but like you said reacts with the air, in this case it would be the water that becomes aggitated, i'm thinking that it's effects would be enhanced as water is denser than air, as was mentioned, so it would be a hotter beam, range would be the same and i think it would yield the same heat problems as plas and las. Firing it into the water would be fine IMO though

Thoughts?

The energy of a photon is inversely proportional to it's wavelength.

I'm sure the cogboys can work their magic on the lasers. Wavelength changes shouldn't affect the intensity AFAIK. Again, as for the plasma and melta weapons, I don't know what would happen.

A bolter round detonates on contact with a change in mass. The standard shells are calibrated to be a change in mass from air pressure. The water pressure inside the barrel would be enough to set off the shell, so unless you are using a specially designed bolter shell you are effectively sticking a frag grenade in your gun.

Hypercavitating bolt shell, and have a safety so that the detonator sensor doesn't activate until some fraction of a second after firing (enough time for the shell to clear the barrel).

If you read one of the Guants ghosts novels there is a chapter where they assault an oceanworld. some no-name ghost got tangled up with a drowned ghost and in his desperation fired his lasgun causing the water to heat up severely. Now I know Dan Abnett is only human and is as prone to mistakes as the rest of us, but he has a good track record for being accurate so i have no reason to doubt that he is correc in this instance.

Mad Larkin states that lasrifles can be fired under whater when talking to the Angel. I might be wrong. I personly think the would, scince lazer doesent create heat until comming in conntact with something non-transparent. I wouldent trust Dan Abnet on fycics however scince well, i think we could agre that las shouldent have recoil + other varios minor faults

Yes but water isn't 100% transparent. Light can only travel for about 40m through water before it is entirely blocked. It would become unefective as a weapon long before that.

I think blue lasers would travel much further through water... read that somewhere discussing possible laser weapons, laser-defense grids and such, can't remember where though.

Las weapons (assuming they really are lasers and not just energy bolts or something) can fire underwater, however their range is severely diminished. The scattering effect of the water means that their range is severely curtailed (doubt you would really be able to kill anything at all unless the weapons barrel was up against the target), and accuracy is pretty much shot to gak as it would beam off at various angles.

Melta and Plasma weapons would kill the firer almost instantly (assuming you could fire them... my guess is that the firer would be dead just from the chargup phase). Containing the energy in a magnetic field doesn't stop energy bleed off (i.e. heat), that would heat the water surrounding the weapon which would in turn heat the water around the firer. We already know that the in the open air the firers of said weapons often describe the intense heat they feel when they use them, this effect would be increased significantly underwater, plus there would be a pressure bubble formed by the steam and... uhhh... it would be a mess...

Bolt weapons would fire, but their range and accuracy would be effected, although the explosiveness of the bolt would actually make them more lethal underwater due to wave propagation, etc.

What about gauss weapons (necrons)?

Gauss = Field manipulation (breaks down the target and draws the subatomic bits toward the gun). I'd say it would work just fine. It looks like green lightning, but isn't Water particles might mess it up, but then air molecules ought to also? Hard to say We don't really have much fluff on them to go by.

Particle whip/staff of light might work Lack of info here.

Underwater Wraiths would be a fun surprise to use

There's a world of difference between the density of air and the density of water though. Necron weapons would probably work fine just because their tech level is basically at the 'it's magic' stage. They have non-warp based FTL and teleportation, they've probably got something that lets them fight underwater.

Who says the density of the material makes a blind bit of difference to the Gauss weapon, though?

We don't know how they work, except that mathematically they shouldn't

Necron tech-so-advanced-it's-magic tech is awesome, mainly BECAUSE it can't be explained If they want to be exterminating all life they'll need to go underwater sometimes

Ascalam wrote:Who says the density of the material makes a blind bit of difference to the Gauss weapon, though?

We don't know how they work, except that mathematically they shouldn't

Necron tech-so-advanced-it's-magic tech is awesome, mainly BECAUSE it can't be explained If they want to be exterminating all life they'll need to go underwater sometimes

I can imagine them working underwater and the necrons would be just like the cursed pirates in pirates of the caribbean, all ominous and being not even mad underwater. Any sea predator wouldn't thoroughly enjoy a mouthful of metal either i can't imagine, unless it's the scrap eating gooberfish

Take a mouthful of tinfoil. Chew it up real good..

Not tasty for most critters, though some (like sharks) don't seem to care overmuch what they swallow

Who says the density of the material makes a blind bit of difference to the Gauss weapon, though?

So far in this thread... no one.

Ascalam wrote:Take a mouthful of tinfoil. Chew it up real good..

Not tasty for most critters, though some (like sharks) don't seem to care overmuch what they swallow

What about a mouthful of gauss
Probably find it a week later when it's caught and cut open: Fisherman cuts shark open, gauss beam comes flying out

And here's one i prepared earlier..


Automatically Appended Next Post:
DaveNYC mentioned that there is a world of difference between the density of air and of water, in passing. That was what i was referring to. He didn't say it made a difference. I theorised that it might affect it in my post just above his, and then it might not

There wasn't an attempt to prove a point there, just bouncing some theory around

Ascalam wrote:And here's one i prepared earlier..


Automatically Appended Next Post:
DaveNYC mentioned that there is a world of difference between the density of air and of water, in passing. That was what i was referring to. He didn't say it made a difference. I theorised that it might affect it in my post just above his, and then it might not

There wasn't an attempt to prove a point there, just bouncing some theory around

Ainsley would still be smiling, even when disintergrated.

OT would the gauss beams stop if it hit tiny things like plankton? Would it stop and dissolve it or use it's magics and keep going, do they just break down whatever they hit?

Beats me

Probably fry it on the way along...