Dept. Of Defence Briefing on Depleted Uranium
NEWS TRANSCRIPT from the United States Department of Defense
DoD News Briefing
COL James Naughton, U.S. Army Materiel Command
Friday, March 14, 2003 -- 1 p.m.EST
(Also participating; Dr. Michael Kilpatrick, (OASD HA) Deployment Health Support Directorate
Slides shown during this briefing can be found on the Web at: http://www.defenselink.mil/news/Mar2003/g030314-D-9085M.html
MODERATOR: Thank you for attending this afternoon. Today's briefing is on depleted uranium. Depleted uranium is
something that I think we have not done a good enough job in making sure that everybody understands what depleted
uranium is and what it isn't. And as we go forward, and if there is a conflict in Iraq, I think it's important for
everybody to have a good understanding of depleted uranium, because there is an awful lot of misinformation out there
about depleted uranium.
To help us do that today we have two briefers. We have Army Colonel James Naughton from the U.S. Army Materiel Command
and he'll talk about depleted uranium as a weapon and as an armor plating. And also with us today is Dr. Michael
Kilpatrick, who is of the Deployment Health Support Directorate, and he will be here to talk to you about the health
effects of depleted uranium. We have probably about 30 minutes or so, but we will try to get all your questions
answered. So let's go ahead and get started. COL. NAUGHTON: I'm Colonel Jim Naughton from Army Materiel Command. I am
currently the director for munitions in that organization. I have been involved in developing and buying munitions most
of my military career.
We have several branches of service that use depleted uranium. We have used it for about two decades. Next chart
please. During the Gulf War, we fired ammunition weighing approximately 320 tons. That sounds like an awful lot of
depleted uranium, but when you actually put it together and measure it, it's a cube about eight feet on the side. It
isn't really a lot of material. Depleted uranium is very heavy. That's one of the things that makes it good for use in
ammunition and armor, so it doesn't take up a lot of space.
Next chart. The Air Force was a principal user during the Gulf War. They fired the ammunition from their A-10 aircraft,
30 millimeter gun system.
Next chart, please. The Army was the second largest user. We fired most of our ammunition from the Abrams tank,
approximately 50 tons, as indicated on the chart. And the remaining 11 tons of ammunition was fired by the Marine Corps,
again principally from tanks and the Harrier aircraft, the AV-8.
Next chart, please. We have two military uses for depleted uranium. The first one is to make penetrators. Penetrators
are what we use to penetrate armored vehicles, kinetic energy weapons like the MA-29 series, ammunition for the Abrams
tank, use the energy that's created when the bullet is launched from the bore of the canon to breach the armor on the
other end. So you want something that's very dense and very hard, so that when it reaches the other end, instead of
splattering like you would expect a lead bullet to do, it actually retains its shape and drives through the target.
Next chart. This is why the U.S. Army prefers to use depleted uranium over tungsten ammunition. If you look on the
chart you can see that the depleted uranium is a material that has a characteristic that allows it to sharpen itself as
it penetrates the target. The uranium shreds off the sides of the penetrator instead of squashing or mushrooming. If you
look at the lower picture, which is what happens with tungsten, the tungsten mushrooms. The result is the depleted
uranium will penetrate more armor of a given character and type at a given range than tungsten will, no matter how we
design the penetrators.
Next chart. Proof is of course in the pudding. These are two high-speed X-ray pictures taken of penetrations actually
going on, and you can see the tungsten penetrator deforming in the bottom picture, and you can see the DU penetrator
maintaining its shape in the top picture.
Next chart. Why do we use it? This is the result. What we want to be able to do is strike the target from farther away
than we can be hit back, and we want the target to be destroyed when we shoot at it. We don't want to see rounds
bouncing off. We don't want to put our soldiers in the position that you see, if you watch "Kelly's Heroes," where they
load tank rounds with paint in order to blind the target. And I'm sure everybody in here has probably seen "Kelly's
Heroes" once, because in World War II we faced a problem of not having the overreach we have today. We don't ever want
to go back to that. And we don't want to fight even. Nobody goes into a war and wants to be even with the enemy. We want
to be ahead, and DU gives us that advantage. We can hit, and they can't hit us. During the Gulf War we had tanks engaged
in situations with multiple Iraqi tanks that were shot, hit -- not penetrated -- and proceeded to destroy all three of
the targets that engaged them, including shooting through a sandbag and destroying one of the Iraqi tanks. It really
happened. That's how much advantage it gives us. So we don't want to give that up, and that's why we use it.
I'll be followed by Dr. Kilpatrick.
MR. KILPATRICK: Good afternoon. It's certainly my pleasure to be able to be here this afternoon and talk with you about
the medical health effects of depleted uranium.
I want to first start by talking a little bit about natural uranium, because I think we need to put it into that
perspective. Natural uranium is in the soil around our world. It certainly is something that we eat and drink and
breathe in every day, because it is in our environment. We all secrete natural uranium in our urine to a certain level.
We know that in some areas of the world there's less and some areas there's more -- particularly say in Florida there's
a lot of natural uranium in the soil. You get into Colorado, you'll find the same sort of thing. You get into other
areas of the world there are variations. And yet we do not see natural uranium causing any recognized medical
complication or health problem in people. We have had a lot of studies in uranium miners. We know an awful lot about
what uranium does as a heavy metal in people, and we certainly have a lot of studies on depleted uranium in the
environment, and I'll talk a little bit later about from the Gulf War some individuals who were involved in friendly
fire.
Next slide, please. Our major concern, as I said, is the chemical nature, because uranium, depleted uranium are both
heavy metals -- like lead and tungsten and nickel. The kidney, when the depleted uranium is internalized, becomes a
target organ, and there are collecting tubules that essentially concentrate the urine that are most severely affected,
the first to be affected if there is a dose of natural uranium or depleted uranium above a threshold in the body.
We looked at some 90 Gulf War veterans who were in or on an armored vehicle when it was struck by depleted uranium in
friendly fire. And those individuals have been followed on an annual basis now we are talking 12 years post-incident.
And we do not see any kidney damage in those individuals -- and this is using very sophisticated medical evaluation of
kidneys. They were also followed for other medical problems, and they have had no -- and I'll talk about this a little
bit later, but while I'm here, they've had no other medical consequences of that depleted uranium exposure. Now, some of
these individuals had amputations, were burned, had deep wounds, so that these individuals, some of them of course do
have medical problems. But as far as a consequence of the depleted uranium exposure, we are not seeing anything related
to that either from a chemical or radiological effect.
Next slide, please. We've looked at them for cancers. There has been no cancer of bone or lungs, where you would expect
them -- to see that. We have seen no leukemias. As I said, there's been about 90 individuals we've followed up, and
about 20 of these individuals still have small fragments of depleted uranium in their body. To try to remove that
totally from their body would mean amputation or removal of muscles. And our belief is it's better to follow them than
to go through any further traumatic type of surgery for the individuals. And, as I've said, we have not seen any
untoward medical consequence in these individuals.
As we take a look at transuranics, and that's been brought up -- you may have heard about that -- these are trace
elements of like Americium, plutonium, neptunium that has been found in depleted uranium in the process of making it. It
goes through the same processing plant where nuclear fuel is reprocessed after it is spent. And there trace amounts of
transuranics in the depleted uranium. It has been looked at, measured by several different countries and scientists
outside of DOD. The amount of radiation that contributes is less than one percent, and that is believed not to have any
medical significance as far as adding to the radiation.
Depleted uranium is 40 percent less radioactive than natural uranium around us. And so when it's outside the body it's
just not an issue. It's only when it's internalized -- either by inhaling the dust, the oxide, as Colonel Naughton said
when there is penetration of armor, it does self-sharpen and it does create an oxide dust. And there are people who were
in or on the vehicles that were struck in friendly fire, who did inhale that oxide, and we have not seen any medical
consequence from that. They certainly had the highest dose exposure of anybody in the Gulf War.
Next slide, please. We talked about not seeing any cancers in the kidney or certainly in the lungs or the bone in these
individuals. Leukemia became an issue a couple of years ago when the Italians were concerned about peacekeepers in the
Kosovo area coming back and having leukemia. We took a look at what are the causes of leukemia. The rates in the United
States are usually about two per 100,000 people per year. Cause of leukemia is often unknown. We took a look at data,
medical data, from the exposures, atomic bomb blasts in Japan in World War II, people getting chemotherapy. We see an
increased rate in leukemia in these individuals, some two to four to six years after that exposure. And we certainly
know people exposed to toxic solvents like benzene can have an increased rate of leukemia. But the Italians did the
epidemiological study and found basically the rate of leukemia in their military personnel was no greater than their
civilian population. And so what was triggered as a cause-effect relationship being in Kosovo where depleted uranium in
was fired was not a causal relationship. It was just the natural rate of leukemia in the people who had been
peacekeepers in that area.
Next slide, please. There have been over 40 tests done on what happens to depleted uranium from an environmental
standpoint, both with shooting munitions through armor, looking at burning of depleted uranium. We had some fires in
tanks. We had some fires in depleted uranium. It was in storage capacities. And we have recently done a capstone study
where we again have shot depleted uranium through uranium armored tanks to look at what is the amount of oxide created,
how long does it stay suspended, what is the particle size. That study has just been completed, but it is not yet
written to be published. When it is written it will be published. All of the environmental information about depleted
uranium is in our Department of Defense environmental exposure report, and I'll have a website that will show you that
at the end of the talk.
We continue to do testing in animals. Some people ask why do you continue to test if you say it's not an issue. I think
if there are questions we need to continue to bore down on the science and make sure that those continued experimental
evidence from animals validate what we know in people. And I think that it's extremely important to say that we are
doing all the tests that need to be done to understand the physiology of exposure to depleted uranium.
Next slide. Recent environmental assessments done outside the Department of Defense. The United Nations Environmental
Programme has put out this book, called "Depleted Uranium in Kosovo," where they went and did soil samples. They went
and looked for the penetrators. Again, these are the A-10 airplanes shooting. They found some seven penetrators or the
sabot, what you saw coming off the round on the ground. These had either hit rocks, cement, and ricocheted. Normally
when an A-10 fires if it hits ground it buries anywhere from one to ten meters deep. But they found seven on the ground,
some 13 tons of depleted uranium had been shot from the airplane in the Kosovo area. And they have not been able to find
any environmental effect of depleted uranium -- not residual other than finding those penetrators lying on the ground.
They've checked water. There have been other countries -- the Belgians came in and looked at food, water, milk, fruits,
vegetables, meat, and essentially were not able to find any evidence of any increased uranium or depleted uranium in any
of those samples.
The World Health Organization has done a similar study in the Balkans. The European Commission, the European Parliament
and the United Kingdom Society for World Society has also published a report on looking at all that data. So we have
outside of DOD, outside the United States, organizations taking a look at what are the environmental effects, and they
are consistent in their finding that there is no environmental effect in an area where depleted uranium has been shot.
Next slide, please. These again are a couple more meetings where they got experts from around the world -- and the last
one, depleted uranium in Kosovo, and that has been published at a meeting in Germany. Again the scientists are in
concurrence that it does not pose an environmental hazard.
Next slide. When DU does strike armor and that oxide is created, it falls to the ground very quickly -- usually within
about a 50-meter range. As Colonel Naughton said, it's heavy. It's 1.7 times as heavy as lead. So even if it's a small
dust particle, it's still very heavy. And it stays on the ground. They've looked on the battlefield in multiple
locations. We looked in Kuwait where we knew that there were tank battles. We looked in the boneyard in Kuwait where all
of the Iraqi armored vehicle that was hit with depleted uranium was dragged, and we were not able to find anything on
the ground around those vehicles that's above background in radiation.
If you look at hole where the depleted uranium round went in and out, there is an increased radiation where that metal
was essentially welded onto the armor. But that's not going to go anywhere. It's not going to fall off. It's welded onto
that armor. And the boneyard is out in the desert were eventually the sand will cover it over. And, again, it does not
pose an environmental hazard.
I think the Kosovo report focuses on picking up lose particles that are on the ground. They need to be appropriately
disposed of and that would be buried at a documented site.
They recommended continuing to look at groundwater. They don't believe that there's a likelihood that that would be the
case. Our studies in the United States over 15 years have not shown depleted uranium going from the soil into
groundwater. It just does not move from the round that is in the soil. And the bottom line is there is going to be no
impact on the health of the people in the environment, or people who were there at the time it was shot.
Next round. We have a lot of information and history medically on uranium which applies directly to depleted uranium.
The Agency for Toxic Substances and Diseases Registry says there has been no documented case of any cancer of any type
related to exposure to uranium or depleted uranium.
Looking at those individuals whom we know were most highly exposed to depleted uranium in the Gulf War are some 90
individuals who are being in the medical follow-up program. They have shown no adverse effect from their exposure to
depleted uranium. And, again, the multiple other organizations reviewing this data are consistent with our understanding
of depleted uranium. It is a superior weapon, superior armor. It is a munition that we will continue to use, if the need
is there to attack armor.
I am going to stop here and see if you have questions. Colonel Naughton, would you join me here for questions?
Q: Well, you just said it but I would like to ask the colonel -- you've implied it, but you haven't said it. I assume
that you fully intend -- if there is a war in Iraq, you fully intend to use depleted uranium.
COL. NAUGHTON: As a practical matter, if we use Abram tanks, we have no choice. We do not have an alternative for the
Abram tank.
Q: And the A-10.
COL. NAUGHTON: And the A-10. Well, the A-10 -- there is an HE [high explosive] round for the A-10.
Q: May I just follow up on that? Actually you had said it's an advantage and we do not want to give it up. Why would it
even be considered that you would give it up? And why are you even saying that?
COL. NAUGHTON: Well, you need to look at the environment of the context where people are asking us questions -- who's
asking the question? The Iraqis tell us terrible things happened to our people because you used it last time. Why do
they want it to go away? They want it to go away because we kicked the crap out of them -- okay? I mean, there's no
doubt that DU gave us a huge advantage over their tanks. They lost a lot of tanks. Their soldiers can't be really amused
at the idea of going out in basically the same tanks with some slight improvements and taking on Abrams again. That has
got to be a huge morale -- so wouldn't it be great if we could convince the world to make the U.S. give up DU?
Q: So it's basically you're saying the Iraqis are behind any sort of effort --
COL. NAUGHTON: And other countries that are not friendly to the United States.
Q: Well, is it a concern of some in the military that they are afraid to use the ammunition because of the -- I mean,
I'm trying to get a sense --
COL. NAUGHTON: I've never met anyone that was afraid to use the ammunition.
MR. KILPATRICK: We have an extensive training program on depleted uranium for military members. The soldiers' common
task manual explains that depleted uranium, if it is used on the battlefield, and you see a tank that has been taken out
by depleted uranium, the first rule is don't go into damaged equipment on the battlefield. That poses a hazard. There
may be unexploded ordnances, there may be other chemicals that were in there from a fire that burned. And if it was
taken out by depleted uranium, there may be oxide that you don't want to inhale. We want to minimize any exposure, at
least to the lowest level as possible. If somebody needs to go into a tank that's been hit with depleted uranium, a dust
mask, a handkerchief is adequate to protect them -- washing their hands afterwards. So the colonel is right, nobody here
has fear of it. But there are people who want to ban nuclear weapons, and they try to link depleted uranium to nuclear
weapons. It's not a nuclear weapon. It is a heavy metal that just happens to be radioactive. It's lower than natural
uranium. It's used in a lot of industrial settings. It's used as ballast in rudders on ships, in airplanes. It's used as
essentially the protective mechanism, if you will, for radioactive medical materials that are used in hospitals for
diagnostic procedures -- kind of a shielding for that high radioactivity, so that it has a lot of commercial use. And it
again is not a hazardous substance.
Q: You mentioned of the 90 Gulf War veterans you are tracking there have been no adverse health effects. Does that
include neurological disorders as well?
MR. KILPATRICK: Yes. And I think Dr. McDiarmid has published on this. What she found in an early test about three years
into her study -- she was using a new neurological test that is computer based, and she found some abnormalities in some
of the individuals that had the highest level of depleted uranium in their urine. When she repeated that test the next
year, the next annual evaluation, she did not find that same effect. So it happened one testing. There was a great deal
made about it at that time, but when she followed these individuals up the next year there was no difference in those
who had the fragments in them with high levels or low levels of depleted uranium in their urine or their counterparts
who did not have fragments and had normal levels of uranium in their urine, with no depleted uranium.
Q: Doctor, you mentioned natural uranium and uranium miners. The federal government is compensating former uranium
miners for health problems that are linked to their exposure to natural uranium. What makes that different than DU?
MR. KILPATRICK: I think the health problems, if you look at that closely, as they are looking at in the mines, the
uranium mines they had exposure to radon. And we know that radon is certainly an agent that can cause cancer. And as
they've taken a look at uranium miners with that radon exposure, that's what that compensation is directed to. The
scientists have tried to say, How can you parse out the natural uranium exposure versus the radon exposure? And they've
done that in looking at radon levels and looking at people handling natural uranium in the milling process essentially.
So that is an area.
Now, recently at Paducah we know that some people working with radioactive materials did handle high-level radioactive
material without knowing what they were doing, and there's a compensation issue related to that. Again, that's not
depleted uranium or natural uranium; that's the highly-radioactive materials that were brought back to be reprocessed.
Q: Just for the average person following up on that, though, could you explain why the soldier wouldn't face radon? I
mean, just for someone who is not following you scientifically?
MR. KILPATRICK: Radon comes out of the ground, and that's why when you buy a house you have got to have [a] radon
[detector] in the basement studied to say is it safe. Depleted uranium is a chunk of heavy metal. It doesn't have any
off-gassing. It doesn't have any gas in it. The radon is not part of the uranium. It's in the same locale, same
location, because it's around the world, natural uranium. So it's a different exposure. It's not connected
scientifically to uranium or depleted uranium.
Q: Colonel, is the U.S. the only country that's developed depleted uranium projectiles?
COL. NAUGHTON: It's not the only country that's developed it. It's not the only country that uses it. But the United
States and Britain are as a practical matter the only people that have manufactured that ammunition that I'm aware of.
Q: There's no chance that Iraq might get their hands on some?
COL. NAUGHTON: Well, they would have to get their hands on some that fit their tanks. And I don't believe they have any
tanks that use 105 or 120 millimeter tank guns.
Q: Could you explain for the layman the process of depleting uranium?
COL. NAUGHTON: Yes, what -- the commonest or best known method is the centrifuge. And what happens is you take
naturally-occurring uranium and you combine it with fluorine to make a gaseous substance called uranium hexoflouride.
And you take the uranium hexoflouride and spin it in a centrifuge at a very high speed. And the U-235, which is slightly
lighter than U-238, separates out. And you do this in a series of centrifuges one right after the other, passing the
most -- more steadily enriched uranium through the process and out one end comes what's called enriched uranium, which
consists predominantly of U-235. It does contain some U-238. And what's left over is uranium hexoflouride gas consisting
primarily of the U-238 isotope. You then extract the fluorine through a series of steps, and what you have left is
depleted uranium metal, which goes by the name of Derby. If you ever read some technical manuals and you see somebody
talking about Derby, that's what they're referring to, and that's because the way we manufacture the metal has a
distinctive shape that looks like a hat.
Q: So it's a by-product of making highly-enriched uranium?
COL. NAUGHTON: And that's why --
Q: -- used for weapons and or anything else?
COL. NAUGHTON: Correct. It will work for reactor material -- primarily for reactor material in this point in time.
MR. KILPATRICK: And just to follow up, you used I think a very appropriate word, as a by-product -- depleted uranium is
a by-product for that process. It is not nuclear waste.
Q: Colonel Naughton, you said a few minutes ago that there were no alternatives to depleted uranium. But are the Army
labs possibly looking at other materials?
COL. NAUGHTON: We will always look for other materials. I want to have the best sword I can get if I am a medieval
warrior. That's why there's the legend of Excalibur or Prince Valiant's Singing Sword. And in today's world we want to
have the best weapon we can get. So we will continue to research and look for alternatives. So far we have come up
empty. But that doesn't mean that 10 years from now there won't be an alternative and we'll switch to it -- not because
we dislike depleted uranium but because we found something better.
Q: What about steel?
COL. NAUGHTON: Steel doesn't work. Steel is not dense enough to do this. If you follow the history of anti-armor
weaponry, the first anti-armor weapons of this type used a steel rod, and then they very quickly switched to tungsten to
form the penetrators, and that happened during the early and middle parts of World War II. By the end of World War II,
armor-piercing ammunition was predominantly made with tungsten. But some of our 50-caliber machine gun ammunition that's
labeled armor-piercing, which is for shooting obviously much lighter targets than tanks, does use steel rod still.
Q: Can you tell me what is the likelihood that depleted uranium weaponry would be used in an urban environment? And the
reason I'm wondering is what the likelihood might be that children could be exposed to this after the fact, no matter
how much care you take in the targeting, a child being exposed to this. And are the levels of exposure for children, the
danger levels of exposure for children the same as for adults?
COL. NAUGHTON: That's a two-part question. Why don't I take the first part, which is likelihood. You use this kind of
ammunition against tanks. So the only reason we would be using it in an urban environment is if our opponents take their
tanks into an urban environment and we have to kill them. So that's the scenario. So is it likely? That depends upon how
the enemy reacts. Tanks are open-country vehicles. They don't do well generally in built-up areas. But they can be used
in built-up areas. That's a tactical choice, and if our opponents take that tactical choice you could see that activity.
And I think the rest of it is --
MR. KILPATRICK: I think as far as health effects on children we do know that, as I said before, if the depleted uranium
is external to the body there is no health effect. What we worry about like lead in paint in housing areas -- children
picking it up and eating it or licking it -- getting it on their hands and ingesting it. And there really is no data on
how much it takes to cause an issue or a problem in children. If you are taking it in orally, most of that is going to
go right through the gut. I mean, they've done studies of this -- of all heavy metals -- and there's very little
absorption of that. And you'd really have to have a very large internalized dose.
Dr. Naomi Harley, when she took a look at inhalation of oxide, said with a concentration that's created even while the
DU is penetrating armor you would have to inhale enough to almost suffocate to get an effective dose. So it's --
Q: -- issue in the past -- children being exposed.
MR. KILPATRICK: It has not been an issue in the past. We really have no data. When we take a look at how much you would
have to internalize, you are not going to get that with casual exposure.
Q: Which depleted uranium armor -- what vehicles use that, and how effective is it against --
COL. NAUGHTON: It's used principally on the Abrams tank. You will find it in other uses. You'll see things called
applique armor people talk about, and it can be used in applique armor for just about any vehicle you want that you want
to hang an armor box on. But our principal use for it is -- our principal use is in the Abrams.
Q: How effective is it?
COL. NAUGHTON: I'd say it's very effective. But to get into how effective with numbers, we start to get to classified
very, very quickly. The fact is that Iraqi tanks -- and this is the way you can judge --
Q: (Off mike)?
COL. NAUGHTON: If you're close enough and live long enough to shoot, yes. But you have got to be real close.
Q: The fact is that Iraqi tanks -- you started to say something about Iraqi tanks.
COL. NAUGHTON: I was going to say the fact is that in the desert in the last war, Iraqi tanks at fairly close ranges --
not nose to nose -- fired at our tanks and the shot bounced off the heavy armor. So -- and our shot did not bounce off
their armor. So the result was Iraqi tanks destroyed -- U.S. tanks with scrape marks.
Q: Colonel, just to go back to what you were saying earlier, the reason you were saying the Iraqis are making a claim
that there were all these adverse health effects is because this is a posture on their part not to be used because --
COL. NAUGHTON: That's Jim Naughton's personal opinion, yes. That's why you'll find people making -- in other
governments making noise about us using it. It's interesting to note that we have sold depleted uranium ammunition to
some of our allies in Southwest Asia, and I don't hear any of them complaining about it.
MR. KILPATRICK: Let me just address the ill people in Basra. It's been in the media a great deal, and reporters have
gone and seen children with birth defects, children with cancer, adults with cancer, with other ills. The World Health
Organization went into that area and took a look at what it would take to do the appropriate epidemiological medical
studies to understand why are people ill in this area of the world. They laid out that requirement of that kind of study
and said the World Health Organization is capable and willing to do this. And the government of Iraq said no. Unless
that study is done, it is going to be very difficult to try to understand what is behind the large number of people
being ill. If you go to the MD Anderson Hospital in Houston and say are people in Houston ill with cancers based on
people coming into a cancer treatment center, you would get a skewed impression of the rates of cancer in Houston. And
so I think when you take a look at Basra it is the kind of medical center in that part of Iraq that anybody who is ill
would gravitate toward that area.
When we take a look at where were the tank battles in the Gulf War, there were no tank battles near population areas.
And, as we said before, this oxide doesn't blow around. It is very heavy, and when it falls to ground it stays there,
and the fact that it moves on down into the sand. So from a perspective of could depleted uranium be playing a role from
a medical standpoint, no. But there clearly are ill people there.
MODERATOR: All right, thank you, all.
ENDS