WWII Smokescreen Development

Vapor, not Smoke

The "smoke" created by this technology was neither a smoke
(like the product of the cumbustion smoke screen methods) nor a
chemical gas (like the product of the chemical smoke bombs) but
was a vapor of a specially designed formula created by Patterson.
This formula was referred to as the Patterson secret formula by
the millitary researchers, but shortly after its implementation, the
composition was known as "fog oil," a name that had not entered
the lexicon until Patterson's invention.

The "fog oil" was atomized by specially designed nozzles,
injected into a heated chamber, then vaporized, but not burnt, by
the hot gasses within. This vaporized fog oil was then ejected into
the air by rapidly moving air flow. Upon entering the air outside the
heated chamber, the fog oil vapor immediately condensed, forming
an extremely thick fog layer that hung close to the ground.
According to one of the Patterson patents, and this was confirmed
by subsequent Navy researchers as reported in this document, ".
. . [the] smoke screen or cloud produced. . . develops a density
and opacity greater than the heaviest known natural fog." A
person need only imagine the thickest fog they have seen or
heard about to realize the enormous obscuring power of this
smoke screen. Objects less than 1 foot within the smoke scren
were completely hidden from view. It was denser and could be
produced faster than any smokescreen ever created.

Troop Health
The Patterson smoke screen system had another great advantage
over all previous smokescreens: it was virtually harmless to
troops. It had no known short or medium term toxicity. Long term
toxicity may have been possible, most likely only with frequent
exposure, but even today, there is no clear evidence of long term
side effects resulting from exposure to this type of smoke screen.
This is why the main ingredients of the formula remained a part of
fog oil compositions long after WWII.

Patterson Obscurant ("Smoke Screen") System
There were several aspects to the Patterson system, all of which
were detailed in his four US patents. First was the fog oil formula
which was comprised of three primary components: an oil base,
an inorganic mineral salt, and a viscosity inducing agent. To this
basic formula were added pigments designed to either whiten the
smoke (as would a pigment such as Titanium Dioxide) or color the
smoke. In addition graphite was often added to prevent valve
clogging. (This graphite was later found to be an effective
obscurant against infrared). The Patterson formula (perfected with
the help of Harold Levy, a chemist) allowed for many different
types of permutations of the basic composition described above.
All was detailed in his patents on chemical composition of smoke
screen and methods of producing smoke screen. All patents
following his--continuing to the present day--use one or more of
the various Patterson formulae detailed in his patents.

Secondy, were the apparatuses involved. There were two types of
apparatuses perfected by Patterson, but each performed the
same basic task, to provide a heated chamber for the vaporizing of
fog oil and to provide a means of rapid ejection of the vapor into
the atmosphere. One apparatus, the mechnical smoke
generator used the exhaust of an internal combustion engine as
a heating heating chamber where atomized fog oil would be
injected into for vaporization. The ejection of the vapor was
accomplished by the movement of hot exhaust through the air
chamber. The hot exhaust gasses, therefore, accomplished two
purposes. Click here to see pictures and technical drawings of the
external combustion engine device. The exhaust type devices
would eventually become he prefered design and would be used to
this day.

The other Patterson apparatus was a furnace smoke
generator, often referred to as a smoke cannon due to its cannon
like appearance. In the furnace design, or smoke cannon, fog oil
was fed into an elongated tube (the "cannon") and was vaporized
by heat generated by propane or other hot gases. The elongated
tube accomplished the same purpose as the exhaust manifold
(heating chamber) of the mechanical generator. Rapid ejection of
gasses out of the tube was aided by air induction ports connected
either to a compressor, or to a compressed air tank. Using a
compressor required some sort of power, and this was
accomplished by a smaller combustion engine. A compressed air
tank did not require power, but it had only a limited supply of
compressed air.

Patterson favored the mechanical generator, and the reason was
most likely that it tended to be more efficient, using only one
mechanism to both eject vapor and vaporize fog oil. (The
principles of this device would later be utilized in 1950s designs
using jet engine heat fed into the "smoke cannon" elongated
chamber. These simple high output units became standard
equipment in the military).