The doctrine covering the CS tanks was to "smoke parts of the enemy force" and so isolate them from the battle[1] so the gun tanks could deal with the remainder with a local, if temporary, numerical advantage[2]
While on most tanks the howitzer replaced the turret armament, on the early marks of the Churchill tank, the howitzer was fitted in the front of the hull which, although it allowed the tank to retain its main gun, limited the range and arc of fire.
Usage
Matilda II Mark III CS, equipped at the HQ level, & by the Australians in the South Pacific[3]
Churchill tank Mk I - mounted low in the front hull - with associated narrowed arc of fire - as supplement to its turret mounted 2-pdr gun. A few Churchill Mk IICS were produced with the howitzer in the turret and the 2pdr in hull.
Valentine tank Mk IIICS - a few produced in New Zealand by taking the howitzer from Matilda II Mk IVCS tanks
^Its ammunition codes are listed in Field Service Pocket Book, Pamphlet No. 9a, dated 29 October 1941. The ammunition is listed in both the anti-tank and field artillery sections.
References
^Mobile Division Training Pamphlet No. 2, Notes on the Employment of the Tank Brigade, War Office, 1938, p. 31
^Mobile Division Training Pamphlet No. 2, Notes on the Employment of the Tank Brigade, War Office, 1938, p. 29