Low-yield weapons are nuclear devices where the plan is to make "smaller" explosions. This
is one edge of the nuclear weapon spectrum. Generally in this context low yield means yields
that are a lot less than the 20 kiloton to be found in a normal fission weapon. These
weapons have yields in the sub-kiloton region. Of course, these explosions are always very
large by comparison with other types of weapon which has an approximately similar size.
They are small only by comparison with the potential megaton abilities of nuclear weapons.
The smallest nuclear weapons employed had
approximately 10 tons of yield (like the American W54
warhead used in the "Davy Crockett"), and were made for
short-range tactical applications or nuclear demolition (for
example to destroy bridges).
It is also possible to make a low-yield weapon by reducing
the efficiency of an existing higher yield nuclear weapon
somehow. However this would be expensive and likely
create a low yield the weapon with unnecessary high mass
A weapon designer could want to optimize a low-yield
weapon if he plans one of two goals: small size or minimize
its cost (minimize the fissile material which it contains).
Typically the majority of weapons try to find a middle
point between these two extreme edges.
To create a low-yield minimum mass/volume weapon it should have an efficient fissile
material (for example plutonium). It should also need a low mass implosion system and a
thin beryllium reflector surrounding the fissile material. Because volume increases together
with the cube of the radius, a thick layer of explosive or reflector around the core adds a lot
more mass than the mass of the core itself.
If a beryllium reflector with thickness of a few centimetres is to be used then the radius of a
plutonium core is reduced by approximately half of the thickness of the reflector. Because of
the large difference in density between these materials, it is possible to achieve large savings
in mass. However, at some point, when one increases the thickness of the reflector it begins
to gather more mass than it saves; this point represents the point of smallest total mass for
Minimum mass and minimum volume designs generally are similar to one another. Using a
hollow core of fissile material would add only a little to the overall volume.
Another way to minimize size is by means of a small explosion in the most efficient way as
possible. It is possible to do this by means of applying the same principles that one can use
for a high efficiency design, but simply by means of reducing the amount of fissile material to
bring down the yield. The larger mass of the implosion system and the tamper and reflector
in this case will lead to larger overall mass and volume, although less fissile material is
It is possible to compress 1 kg plutonium to produce a yield in the range of approximately 1
kiloton using a more complicated flying plate design for the implosion system. The use of
this design determines the types of fissile material which is to be used. The high compression
suggests accurate neutron initiation timing. It is possible to produce yields greater than 1
kiloton with this system as a result of fusion boosting.
The American M-28 or M-29 Davy Crockett Weapon System was a tactical nuclear gun
(recoilless) - it was used to fire the M388 nuclear projectile. It was deployed by the
Americans during the Cold War and carried the name of the American soldier, congressman,
and folklorists’ hero Davy Crockett. It was one of the smallest nuclear weapon systems which
America developed the weapon in the late years of the 1950s for use against Soviet troops,
in the case of war in Europe.
The M388 nuclear projectile had a version of the American W54 warhead, which was a very
small fission device with a yield less than one kiloton. The W54 weighed approximately 23
kg, it has a selectable yield which was equal to 10/20 tons. This is very close to the minimum
size and yield for a fission warhead. The complete round weighed only 34 kg.
It was 79 cm long and had a diameter of 28 cm at the most wide point. To fire troops
inserted a subcaliber piston at the reverse end of the shell into the launcher’s barrel. The
piston was thought to be a spigot before the discharge of the propellant cartridge in the
recoilless gun chamber of the Davy Crockett. The M388 nuclear projectile was mounted on
the barrel-inserted spigot by means of slots. After the propellant was discharged the spigot
became the launching piston for the projectile.
The W54 warhead likely was an almost minimum diameter for a sphere implosion device
(the Americans conducted tests of a 25 cm implosion system however).
The test devices for this design fired during Operation HARDTACK Phase II (tests codenamed
Hamilton and Humboldt on 15 October and 29 October 1958) weighed only 16 kg. These
devices had dimensions 28 cm by 30 cm. Humboldt had PBX-9404 as the explosive.
In the late years of the 1970s, Polish scientists described an advanced "bi-conical"
configuration which was able to compress small amounts of uranium or plutonium by factors
of five to seven. It could also reduce the critical mass to between 50 and 100 grams. Fissile
cores of 200-400 grams could be able to produce one or two kiloton yields. This method is
potentially an increase of an order of magnitude with regard to efficiency in comparison with
traditional implosion methods which are used in nuclear weapons.
Variants of the W54 warhead were also applied in the Special Atomic Demolition Munitions
(SADM) project. SADM was a group of man-portable nuclear weapons which the American
military had in the 1960s. The Americans never used them in combat situations.
H-912 transport container for the Mk-54 SADM
The so-called "suitcase nuke" is a tactical nuclear weapon for which a suitcase is the method
of delivery. It is also sometimes called "backpack nuke", "mini-nuke" and "pocket nuke".
The Americans and the Soviet Union have admitted the production of nuclear weapons
which were sufficiently small in order to be placed in special backpacks during the Cold War.
However, they have never openly admitted the existence or development of weapons which
were sufficiently small in order to be placed in normal-sized suitcases or briefcases. Reports
also say that Israel has produced nuclear warheads to place into suitcases.