Gas! Gas! Gas!

Some two years ago I posted an article which mentioned a Project D.30. This was an attempt to fit a WASP flame throwing equipment to a Sherman tank. In addition, it was considered for firing chemical agents as well. The link can be found here:

https://overlord-wot.blogspot.com/2016/08/vehcile-of-fire-part-two.html

Well I recently read some documents that discussed WASP flamethrowers using chemical weapons and the trials that were carried out. These seem to pre-date, or at least coincide with Project D.30, so it is possible the two were connected.

In early March 1944 Porton Down received a pair of Universal Carriers fitted with WASP flame-throwing gear. These were both a MK.I and a MK.II versions. Both were modified for the trials. They simply had the electrical spark ignition system on the flame gun disconnected, which would normally ignite the flame fuel. A further change was to the Mk.II which had a different nozzle put in place. As the Mk.I didn't have a nozzle it was left unmodified.

WASP Mk.I

WASP Mk.II

As well as the nozzle the other difference between the two marks was the Mk.II had a slightly lower operating pressure (280lbs/sq in vs 250lbs/sq in) and a sight for the gun. The two fuel tanks contained 60 and 40 gallons and were pressurised by carbon-dioxide cylinders.
The main and obvious difference between the two marks, however, is the flame gun mounting itself. The Mk.I had a boom attachment that the gunner moved to aim the weapon, the Mk.II had a weapon identical to the Crocodiles flame gun.

The Mk.I's mounting had an extra valve on it, which was located on the pintle mount. During the course of the trials this began to leak slightly so a drip tray was fitted. Equally after repeated shots with thickened liquids a film began to form on the valve preventing it from closing properly. The simple fix for this was to clean the valve each time the tanks were re-filled. The re-filling process was done exactly the same way for gas or flame, the tanks simply had the liquid poured in.

The ranges achieved were also remarkably consistent with those achieved by flame fuel. Maximum range for the Mk.I was about 60 yards, with 70 for the Mk.II. The optimum range was found to be about 40 yards for the Mk.I and about 15-20% further for the Mk.II, depending on the exact chemical mix. One curiosity was using a thickening agent only affected the liquid at closer ranges to the vehicle, unlike with flame fuels, which get improved range from thickening. When thickened the jet quality became less diffuse and the minimum range was decreased. But even without thickening no appreciable amount of liquid struck the ground within 20 yards of the firing vehicle.

After carrying out range trials a sandbagged bunker was created, with a lot of its mass below ground and a firing slit left open. This was used at a target with a range of 30-35 yards. Several shots were required to get a hit on the aperture, but when they did the results were quite lethal. 
In the first trial a gas identified as "MS" was used. I've been unable to identify which chemical this is exactly, so if anyone can answer that, let me know please. This was enough to cause 100% casualties from skin burns to anyone inside the bunker within twelve minutes. Even those wearing respirators would be killed.

In a second trail hydrocyanic acid (also known as HCN or "AC") was used. Within fifteen seconds a peak of measurement of 112,000 mg per cubic metre were recorded. This would have been fatal to anyone within the bunker, even if fully protected by respirators. This was still the case after two minutes when a hatch way was opened to allow the gas to evaporate. Even after some 19 hours measurements were showing a lethal dosage inside the bunker, although at this point it is likely that gas masks may have offered some protection.

The WASP Mk.I and its crew showing the heavy contamination...

...and the relatively uncontaminated WASP Mk.II and crew.

A final series of trials were carried out to test the contamination of the vehicle and crew. The liquid gasses had red dye added, and the crew and vehicle were covered with a white sheet. It became clear that both the vehicle and crew would become contaminated. If a persistent agent was used this would be quite an issue. However, with non-persistent agents such as "AC" the concentrations would be low enough that the crew could survive with protection.

Image credits:
National Archives.