Report of Subcommittee of the S-1 Committee on the use of
radioactive material as a military weapon.

A.  Availability of Material

1.  There can be no question but that it is now
possible to prepare large quantities of radioactive material
in connection with the operation of what is known as either
the graphite or the heavy water pile.  As the plans now
stand in the United States, it should be possible when the
full units are in operation along these lines to produce
approximately the equivalent in radioactive effect of one
ton of radium every four days.  Since the material produced
is approximately 100,000 times more active than radium
itself, the actual quantity of material produced will be
very much less than a ton, indeed will only be approximately
20 grams in the pure state and not more than 100 lbs. in the
impure form in which it might readily be obtained as a by-
product of the pile.

There is no way of estimating accurately what the
Germans may be able to do, but is entirely possible that
they may soon be in a position to produce similar material,
though probably not a the rate indicated.  There can be no
question but that it would be much easier to produce this
radioactive material than to isolate and purify the final
product from one of these piles in order to make a high
explosive bomb.  Therefore, it the tactical and strategic
advantages of using radioactive material appeared to be very
great, one might expect the Germans to use their knowledge
of applied nuclear physics to this end even if they had not
yet been able to accomplish the production of a usable
atomic explosive.

B.  Contamination of Large Areas of Enemy Territory

2.  On the basis of the present available information,
it has been estimated by those who are most familiar with
biological effects of radioactivity that if the equivalent
of a ton of radium (which in scientific terms is called 106
curies) were uniformly distributed over an area of
approximately two square miles of open
fields,1 the area so contaminated could not be occupied by
human beings with safety except for short periods or time.
Based on calculations and on some preliminary experiments
carried out on a small scale by Dr. Stafford Warren, it
would seem that the radiations over such territory would
correspond to approximately 50 to 100 roentgen units per day
at the height of one meter above the ground.

In an area so contaminated, exposure for a few hours
would probably produce little or no effect, but exposure for
one day would give temporary incapacitation for a large
fraction of those so exposed; exposure for two or three days
would give prolonged incapacitation and in some cases death
would ensue.  The area would be lethal for those who
occupied it for more than a week.  Hence, evacuation would
be necessary.  Since the effects of such exposure are
delayed by days and sometimes weeks, the weapon would be of
little value as a means of quickly putting out of immediate
action those who were exposed.  On the other hand,
extraordinarily high concentrations might cause symptoms to
appear in a few hours.  For example, concentrations five to
ten times the amount considered in the preceding paragraph
(i.e. 500 to 1000 roentgens per day) would be lethal in a
day and would seriously incapacitate after a few hours'
exposure.  These concentrations could be distributing 106
curies over 0.2 to a half of a square mile.  The
availability of material, however, might limit such heavy
dosage to something like two such applications per week or
the equivalent.

Areas contaminated by radioactive materials would
continue to be dangerous until the natural decay of the
radioactivity had lowered the radiation to a safe point.
With the materials in view, this would require many weeks if
not months.

This persistence of contamination in spite or all efforts to
decontaminate constitutes the chief tactical advantage of
this weapon as compared to contamination with mustard gas or
lewisite.  If the surface were hard, some decontamination
might be accomplished by washing with large volumes of
water, but in general it may be stated that no general
method of decontamination appears possible.  A secondary but
perhaps almost equally important advantage of radioactive
material lies in the fact that it would be impossible to
develop protective clothing which could be worn by those who
were to occupy or traverse the area so contaminated.  Here
again the difference between radioactive material and such
poison gases as mustard gas and lewisite is evident.

C.  Radioactive Gas Warfare

3.  In the preceding two paragraphs, we have considered
only the use of radioactive material from the point of view
of contamination of an area.  The effectiveness of such
contamination arises from the fact that the radioactive
substances give off penetrating gamma radiations more or
less equivalent in their biological effects to x-rays.  A
somewhat different use or the radioactive material would
depend on the fact that extremely small quantities of
certain of the radioactive elements appear to be absorbed in
the lungs of animals and produce fatal effects after a
period of some weeks.  The amounts necessary to produce
eventual death under such conditions are extraordinarily
small.  As little as a total accumulation in the lungs of
radioactive material of only 10-6 grams would be fatal.
This means that if such materials could be kept in the air
in the form of a fine dust or smoke in concentrations as low
as two thousandths of a microgram per liter, inhalation of
such atmosphere for one hour would be sufficient to
establish) a lethal concentration; the material would
accumulate in the lungs and the individual would eventually
die of the radioactive poison.  There is no known way in

which such a contaminated individual could be successfully
treated once he had thus' been exposed.  These results in
regard to the effect of inhalation of radioactive dust are
based on preliminary measures and cannot be considered as
final. Nevertheless, they are so striking as to deserve
careful consideration.

The particular elements which appear to accumulate in
the lungs constitute a major portion of the radioactive
by-product of the piles.  Wile a gas mask with a good filter
(the standard combat mask today) would eliminate almost all
the radioactive dust from the atmosphere and thus provide
protection, two alarming facts must be borne in mind.
First, the concentrations we are considering are too low to
be seen and the material is odorless and without taste, so
it would be difficult to know when to "mask up"; second,
even the best masks will allow the penetration or a 0.1
percent or dust if the particle size is about 0.2 microns.
Therefore, with concentrations of one microgram per liter
(still invisible), an hour's exposure (1000 liters
inhalation) might be fatal even with the best mask.  Oh the
other hand, there is fortunately one offsetting factor; a
dust as fine as 0.2 microns per liter and a concentration of
the order of 1-10 micrograms per liter could behave
essentially like a gas.  The material would not settle but
would disperse with winds and temperature differential just
as does phosgene.  Therefore, all the difficulties of
"keeping up concentrations" for more than a few minutes
familiar to those concerned with gas warfare would be at
hand.  It is the long delay in the effect of the material,
however, which would be the chief factor in militating
against its use as a poison gas.

D.  Offensive Uses by the Enemy

4. From the above very brief summary or the essential
elements in regard to the use or radioactive material in
warfare, the following points seem clear in regard to the
possible offensive use of such a weapon:
(a)  The use of the material to produce the maximum
eventual fatalities would consist in developing ways
and means of keeping in suspension in the air in the
form of very fine dust or smoke certain of the
radioactive materials.  But it is not an easy problem
to devise munitions capable of setting up such clouds
of dust or smoke and difficult to keep such clouds from
dissipating.  Furthermore, the fatalities from
radioactive gas warfare would not develop for some
weeks, and therefore while the eventual effect on the
enemy might be catastrophic, immediate effect on
fighting troops would be small.

(b)  The use of radioactive material to cause the
maximum immediate military effect would appear to lie
in the possibility of the contamination of open ground
to give sufficiently high radiation over an area to
render the area uninhabitable.  The chief problem lies
in devising suitable munitions which would give a
fairly uniform distribution of the radioactive material
over the ground chosen for contamination.

It is clear that if the contamination is to be
effected from high altitudes by bombs dropped by
planes, a difficult problem is at hand.  In the first
place, each bomb must be heavily shielded with lead in
order to protect the crew of the plane and those
handling the bomb on the field when the plan is loaded.
It has been estimated that 310 lbs. of lead would be
needed for each bomb carrying 10,000 curies.  (The
contents of such a bomb is uniformly distributed could
contaminate approximately 250,000 square feet so that
the radiation was the order of 100 roentgens per day
and the area uninhabitable except for a few hours.)  It
is evident that in order to have such a bomb distribute
its contents in the form of a dust over an area would
require (1) carefully regulated methods
of ejecting the contents a certain distance above the
ground, and (2) the control of particle size so that
the dust would settle rapidly before dissipation by air
currents.  The radioactive material would be mixed
with, say, 50 kilos of inactive solid material for each
bomb of 104 curies and the particle size regulated by
grinding to 5-10 microns.  The bomb  should be arranged
to burst i the air a thousand feet above the ground
with as low a wind velocity at the time of attack as
possible.  It has been estimated that under those
conditions with zero wind velocity the area covered
would be of the order of magnitude required,- namely,
250,000 square feet.  On the other hand, with a wind
velocity of 5 to 10 miles per hour dissipation would
result in the dust settling over 50 to 100 times as
large an area with the resulting 50 to 100 times lower
concentration.  This wide area would be so lightly
contaminated as to be habitable for many days or
perhaps without serious damage to personnel.

It is clear that if one proposed to contaminate an
area as large as two square miles or so by the use of
such bombs, some 80 to 90 bombs would have to be
dropped at nicely spaced intervals so that there was
neither an overlap nor great areas in between each bomb
pattern, and the meteorological conditions would have
to be accurately estimated in advance.  The tactical
problems involved in accomplishing any such bombardment
from the air at high altitudes are obviously very

The above statement of the problem represents the
simplest case where contamination of open fields or
areas is under consideration.  For built up sections
where a considerable amount of concrete or brick or
tile is used, a much less favorable situation exists
from the point of view of
one desiring to use this weapon.  Dr. Stafford Warren
estimates from his experiments that something
approaching 100 times greater concentrations would have
to be set up in such built up areas in order to be as
effective as in open fields.  If one goes to such
concentrations, it seems clear that the capacity for
producing the radioactive poison might be the limiting
consideration, though one must also consider that the
number of bombs and planes would also go up by a factor
of 100.

The use of much larger bombs that those carrying
104 curies would be difficult because of the necessity
of cooling down large amounts of the radioactive
material which tend to heat up because of the energy
involved in the disintegration which is proceeding all
the time.

(c)  From considerations of (a) and (b) above,
it is evident that considerable experimentation with
actual field trials would be necessary to determine the
optimum conditions under which radioactive dusts could
be disseminated either for lung contamination or ground
contamination.  Such tests could be very readily
carried out by using very small amounts of radioactive
material (tracer amounts) and studying the
concentrations in the air or on the ground by means of
sensitive physical instruments which are now readily
available.  It is the recommendation of this Committee
that if military authorities feel that the United
States should be ready to use such weapons in case the
enemy started to use it first, such studies should be
initiated immediately.  These studies could be carried
out best by a group containing some men who are
familiar with the particular project which is planning
to produce this radioactive material and others drawn
from NLRC who are working on the development of
munitions for dissemination of dust and liquids and
still others drawn from NLRC who are familiar with the
filed testing of chemical warfare agents.
(d)  To the writers of the report, it appears that the
difficulties of devising munitions to produce
satisfactory concentrations of radioactive material
over enemy territory from planes are very great, so
great in fact that it makes the use of this weapon in
this form by the enemy with significant military
effectiveness a rather remote possibility.  In the
hope, however, of a great psychological effect, such
use by the enemy might well be undertaken.

A much easier way of employing the same basic
principle would be to use radioactive material to
render unsafe territory evacuated i the face of the
approaching enemy.  In this case, the dust could be
uniformly distributed over the ground either by (1) low
flying planes, (2) actual spraying of buildings,
streets, air fields and railroad yards from automobiles
carrying lead coated tanks of a solution of the
material, or (3) by land mines (lead coated) which
could be properly spaced and set off at a distance.
The chances of the Germans using some such method of
radioactive warfare seem to the writers of this report
much greater than the other possibilities and, indeed,
sufficient to warrant defensive procedures being
instituted at once in armies planning to pass over
territory evacuated by German troops.

E.  Defensive Measures

5.  The writers of this report feel that from a
defensive point of view, one can consider it unlikely2 that
a radioactive weapon will be used against the continental
United States.  They further believe that if such a weapon
were used against a populated industrial city such as
London, an automatic alarm would be provided by virtue of
the fact that a concentration of material sufficient to

cause serious damage to any portion of the population in a
few hours would also fog all photographic films and give
strange effects in various pieces of physical equipment in
the scientific establishments of the city.  If the material
came down from the air as a cloud of dust, it would also
probably produce strange effects in the radar equipment.
Therefore, special precautions for alerting a city such as
London would not seem very difficult to arrange.  it is
clear hat if radioactive material is found after a bombing
raid prompt evacuation, together with the issuance of gas
masks with suitable filters (the regular Army mask not the
civilian mask) would be in order.

The eventuality outlined above in 4(d),- namely,
use by the enemy of such material to render evacuated areas
uninhabitable,- seems to us sufficiently great to warrant the
issuance of special instructions to at least one officer in
each division of any Army which might be faced with such an
eventuality.  Such an officer should be familiar with the
ways of detection and understand  the reading of certain
instruments which would give the effective radiation and be
prepared to advise on the movements of troops in such a way
as to avoid more than a passing exposure to high radiation.
It would also be of great importance to see that the troops
were equipped with the proper type of gas mask and that
these masks were put on immediately so that dust could be
kept out of the lungs.

Methods of detection based on physical instruments are
open to certain objections, since all such instruments are
somewhat fragile, and may go wrong in the field through the
breaking of tubes, running out of dry batteries, etc.
Nevertheless, such instruments would be the only way of
controlling evacuation of areas intelligently.  They alone
could give accurate readings on which judgment must be
based.  The use of photographic detectors are much simpler
and for the purposes of qualitative detection leading to an
alarm would be very effective.
It is our recommendation that a special committee
composed of Dr. Stafford Warren and Dr. R. S. Stone be asked
to prepare a report on both the use of detection in the
field and instructions which might be issued to a divisional
officer explaining under what conditions troops might be
moved through various areas and what methods of
decontamination could be tried under certain special
circumstances.  In short, this committee should prepare a
manual outlining a doctrine somewhat similar to that which
already exists for the use of gas officers.  It is our
suggestion that either a divisional gas officer or some
special officer attached to the corps of Army headquarters
be charged with the responsibility for these defensive
measures.  Such officer or officers would need to have
instruments available and be given authority to traverse all
areas which previously had been occupied by the enemy to
test possible radioactivity while such areas were being
occupied by our own troops.3

F.  Probability of Use by Germans

6.  Finally, we may venture a few remarks on the
probabilities of use of radioactive warfare by the Germans.
On the factors which make such an eventuality probable, one
must say that as a method for rendering evacuated areas
uninhabitable the weapon seems to have considerable
potential possibilities, provided sufficient quantities can
be produced.  If the Germans could produce at the rate
estimated for the United States, it would be possible for
them to contaminate effectively approximately four square
miles per week.  While this is not a very large amount of
ground, the contamination of small critical areas such as
airports and railroad yards might be of determining
significance.  If the enemy were successful in devising

methods of keeping the radioactive material in the form of
fine dust over a long period of time and therefore use
methods 4(a), then the weapon becomes a form of poison gas
warfare and might be many more times as effective.  Unless
our troops were promptly "masked up," the eventual
fatalities might be very serious.  On the other hand, the
delayed effect seems to mitigate against the use of this
particular weapon.

The direct use of it as a destructive weapon against
such a city as London seems to us extremely remote because
of the large quantities of material which would be required
for any effective concentration.  Because of the shielding
effect of buildings, concentrations in built up areas would
have to be probably 100 times greater than those in open
fields on which we based the statements made in first part
of this report.  On the other hand, the effect on the morale
of the population might be considerable and the possibility
of creating panic would always be in the minds of the

It the Germans were to use this form of warfare, it
would be self-evident that ordinary gas warfare would be
used in retaliation, and with the control of the air in our
hands, it would seem rather a last resort for the Germans to
undertake such a venture.  Of course, the controlling
factor, which none of us can tell, is where the Germans
stand on the manufacturing aspects of this problem.  We can
only state with definiteness that there is a possibility if
not a probability that they are now fairly well along on
such a procedure.  Weighing all the pros and cons, it is the
view of the writers of this report that on balance it would
be unwise not to have some precautions taken by invading
armies even if the possibility of radioactive warfare being
used against them is exceedingly remote.

James B. Conant, Chairman

A. H. Compton

H. C. Urey

Made Series B 11-10-43 3 copies
copy 1 -- Col. O'Connor -- 11-10-43
copy 2 -- Dr. V. Bush   -- 11-11-32

1 Uniform distribution is assumed for purposes of
calculation.  Probably two or three times the area would be
effectively contaminated if the distribution were spotty,
out the highly active spots were not too far apart and the
intermediary zones had some activity.  On the other hand, if
the lack of uniformity corresponded to highly active areas,
a few yards square every half mile the area would hardly
been effectively contaminated.

2 The Chairman of the Subcommittee, James B. Conant, feels
that it is extremely unlikely that a radioactive weapon will
be used against the U.S. and unlikely that the weapon will
be used at all.

3 Two of the signers of this report, A. H. Compton and H. C.
Urey, feel that the immediacy of the danger is sufficient to
warrant a recommendation that in addition to providing
divisional officers properly equipped and instructed,
detecting devices shall be placed with each unit of one
hundred men.

4 Two of the signers of this report, A. H. Compton and H.C.
Urey, desire to strengthen the recommendations of this
report and emphasize their feeling of urgency by inserting
the following to which the Chairman of the Committee cannot

"For its psychological effect, use of radioactive
poisons by the enemy before they expect us to be ready would
presumably be the preferred strategy.  An estimate of the
best time schedule possible for the Germans indicates that
they might possibly be ready to use radioactive materials in
quantity by the autumn of 1943.  Thus an attack within the
next few months may be expected if it is to be made at all.
Immediate preparations for reply accordingly become
important unless there are reasons, unknown to us, for
discounting the probability of use of radioactive warfare by
the enemy.

"Perhaps the most effective reply would be to answer
immediately in kind.  This would warn the Germans that we
are prepared for their "surprise" with the implication that
we will follow through as far as is necessary for victory.
If theirs is a hope borne of desperation, such a reply might
lead to early surrender.  An effective reply which could be
ready by December, 1943 would be several bombs of 10,000
curies each prepared at the Clinton plant.  The preparation
of such bombs would retard perhaps by a few days the
development program for 49 production.  This procedure would
require consultation with an expert on aerial bombs,and
preparation to extract and deliver the radioactive material
in the needed form.  Immediate action is necessary if such
devices are to be available before the end of 1943."



No information has been uncovered which would indicate
that the Germans could not produce radioactive materials in
sufficient quantity by December 1943 to use them as a
military weapon.  If they did so, they could force
evacuation for a period of at least a week of areas of
approximately two (2) square miles every four days.  The
areas could be an occupied city such as London or an
important military point such as a railroad junction.  It
would not be practicable to decontaminate these areas.  Only
time could decontaminate the area.

While it is extremely unlikely that a radioactive
weapon will be used against the United States territory and
unlikely that the weapon will be used at all, still
preparations must not be neglected against such a


1.  That a small group of officers be trained o the
technical aspects of this phase of warfare and then attached
to American Headquarters in London in order that they can
give prompt information in the event of any real or
suspected use of this material by the enemy.  These officers
should do this as an additional rather than a primary duty.

2.  That we continue to improve methods of detection
and protection.  The first of these recommendations would
require the approval of the Chief of Staff.  The second is
now being carried on under my direction and will continue to
be carried on unless instructions are received to the

3.  That we procure and maintain a small number of
portable detection equipment [unable to read].