Varley Smoke Bomb

[Eggs a Cook]

I have come across a reference to the firing of Varley Smoke Bombs from Stokes Mortars by Australian Forces on the Western Front. I am hoping someone has an indication of what the average burn time was for one of these rounds and what area they would have covered?

Thanks

[centurion]

Is this the attack on Hamel? In this case the Stokes were 4 inch mortars operated by the British 1st Special Company attached to support the Australian Infantry, 20 being used. However they were using a new propellant which was defective in many cases. Most smoke was actually fired by other types of artillery. However the ground was so dry that large amounts of dust were thrown up and one commentator suggests that it would not have mattered if none of the smoke rounds had worked as the clouds of dust did the job anyway

This is what the IWM has to say about the 4inch stokes and smoke

" Eventually this mortar (Stokes 4 inch) became the standard type for discharging smoke and chemical bombs and was, in fact, invariably used for these and incendiary bombs

The ammunition consisted of a papier-mache shell attached by a short sheet-iron casing to a gun-metal firing case. The filling was red phosphorus in a cylindrical tin container. In view of difficulty experienced in ensuring a central blow to the percussion cap, a striker-clip designed to slip over the head of the propellant cartridge, which was thus fired by the striker of the clip upon the impact of the bomb with the bottom of the mortar tube. The parts for 10,000 shells were sent to France and assembled at Advance Headquarters of the First Army. This was the first use of the 4-inch Stokes Mortar in battle. During 1916, the bomb was designed in steel and afterwards in cast-iron for simplicity of manufacture. The weight was 26 bs and the maximum range 1060 yards."

Area covered was very dependant on factors such as wind speed and direction and the rate of fire that could be achieved so as to allow a cloud to be built up and persist. I've seen an inter war report that recommends 10 rounds a minute per mortar in relatively still air to build up an initial cloud.and that when white phosphorous was used it tended to "column" rather than spread and was best used for target marking for other artillery.

[Eggs a Cook]

I came across the reference in relation to the 11th Australian Light Trench Mortar Battery firing in support of the 3rd Division's feint on 31 Jul 17 to the East of Messines. The original fire plan called for them to maintain a smoke barrage for 1 hour and 50 minutes after Zero hour, however they were the target of effective counter battery fire after each tube had only fired 20 rounds.

With a rate requiring 10 rounds per minute to establish an effective screen, I can't imagine that they would have been able to achieve much after only 20 rounds from 4 tubes. Thanks for the info.

[centurion]

The 3 inch Stokes was deemed inadequate for smoke and chemicals as the 3 inch round it didn't have sufficient capacity, given the available chemicals, to allow a cloud to be built up and sustained hence the 4 inch Stokes which AFAIK was operated by specialist units such as the special companies. The Australians did use the 2 inch toffee apple mortar for smoke and some OrBats show some of these being retained long after they were supposed to be obsolete

[centurion]

Tactical notes issued by the Australian 13th Infantry Battalion in Sept 1917 indicate that the Varley bomb was an "improvised 3 in Stokes mortar smoke bomb" and useful not so much as a means of laying a covering smoke screen but rather of blinding specific strong points when attacking them. This would not require such a concentrated and sustained smoke bank. Presumably it was improvised as there was no standard 3 inch smoke round. Other Australian war diaries indicate that they were filled with S Smoke Mixture which was a standard British smoke mixture used in various grenades, shells etc. It would seem that the bombs were used in trench raids to smoke out dugouts as I've talked about in another thread.

[Eggs a Cook]

Centurion once again thanks for your help, I had no luck finding any specific details of the Varley bomb through general searches of the AWM and wider internet. The task allocated to the 11 LTMB on 31 Jul 17 does seem to fall within the scope of the guidance given in the source you found, they were tasked to suppress a series of enemy machine gun posts on the right flank of the 11th Brigade’s feint. These posts were located in a series of fortified shell holes forward of the main German line, so I imagine that more concentrated smoke mission would have been desirable over a wide screen that the larger supporting Artillery would have been capable of providing.

[centurion]

The tactical notes I've quoted above do specifically mention increased German use of fortified shell holes and the need to give them individual attention rather than relying on a general barrage to deal with them.