Photograph from The Churchill Tank and Churchill Infantry Tank 1941-51

On hard, dusty ground the Churchill’s ‘sirocco’ fan would send a blast of
dust under the stationary vehicle’s belly and then draw it in through the hatches.

With the early Churchills a combination of a powerful fan, 5 inch outlet with narrow internal ducting and rear hull profile, resulted in dust being blown back under the tank. The volume of dust thus generated was lessened by one of the the improvements introduced as part of the initial rework scheme. Churchills delivered to units had a baffle fitted to the rear output to direct the airflow backwards rather than straight down, and with an 8 inch air outlet with the inner ducting removed altogether which reduced downwards pressure considerably.

The Churchill's principal dust problem occurred when tanks were in motion, not stationary, tracks having the tendency to pick up dust on the way up to idlers. Except when driving in a strong cross-wind, usually dust was fairly evenly dispersed, however, as the tank in the photograph is sheltered on her port side by trees, the pattern depicted in the photograph is probably due to her following too closely the Churchill in front.

Extract from The North Irish Horse - A Hundred Years of Service

Page 120, Footnote 7
An unconnected feature of the Churchill’s cooling system was that, while stationary on hard and dusty ground, the fan would blast dust under the vehicle’s belly before drawing it in through the hatches, causing great discomfort to the crew, particularly the driver and co-driver. To minimise this problem, rolled anti-dust aprons were slung across the bow plates and could be lowered when tanks were likely to remain stationary for any period.

This is probably gleaned from books by Bryan Perrett and is incorrect. None of the NIH Churchills had 5 inch outlets. Two MkIIs, sent to Egypt to test Churchill performance in the desert, finding dust being thrown forward by tracks and into the driver's compartment, attempted to solve the problem by fitting canvas "dodgers" which were lowered while in motion, not when coming to a halt, at best was an unsatisfactory solution.

One of the two Mark IIs sent to Egypt

As the decision to send these Churchills was made in 1940 it is probable they were not reworked, As can be seen, the dust is distributed to both sides and ss it is depicted in motion the 'sirocco problem' is not existant.
    

NIH Churchills at Hunt's Gap, Tunisia.

While it is likely that some of 25th Tank Brigade's Churchills that were shipped to North Africa had not been reworked, when it was found that the amount of dust thrown up was manageable the "dodgers" were removed

My thanks to Chris Shillito for providing the techical informatiion.

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