The Vickers S gun was a 40mm anti tank gun used on Hurricanes in the North African Theater in WW2.  The gun was originally developed by Coventry Ordinance Works as a heavier caliber aircraft guns.  This 37mm C.O.W. gun originally used one pound shells, but by the end of WW1, the 1 1/2 pounder was standard (37X190mm), but the war was over and barely saw service.  The original gun was used during the lull between the wars in experimental fighters, like the Westland COW Gunfighter, and on flying boats.  In WW2 it was used as airfield defense in stationary mounts or in trucks, like the Armadillo armored fighting vehicle (or big truck with a big gun).

Westland C.O.W. Gunfighter

Vickers S gun

When Vickers absorbed Coventry Works, they used the 37mm gun as the basis for their own 40mm S gun, basing the ammunition  on the Navy's 2 pounder anti-aircraft shell.  The gun was mounted on the Hurricane and it shone in the anti-tank role.  Trials found at least a 25% rate of hits against tanks, whereas later in the war, it was found that anti-tank rockets had a miserable hit rate.  The gun used 15 round drums and had a rate of fire of 100 rpms.  The Hurricane was already a serious weapon, with the Mk 2B able to carry 12 .303 machine guns and bombs, the Mk 2C carried 4 20mm guns, and the Mk 2D used with 2 Vickers S guns, along with a .303 gun on each wing to help with aiming.  Lastly, the Mk 4 was the first aircraft to use air to ground rockets.  The British finally let the Hurricane go in 1947.