A good article and for sighted for 1939 and when you consider the problems that the UK had, worth consideration.
The 23mm Marsden sounded like a good weapon.
It was tested by several countries in various installations, but only saw service in a handful of Hawk 75 planes in China and Argentina, I believe.
The gun and ammo were both modified from the popular 20mm Madsen. The 23x106 ammo is shown in the pic below (from the Ammunition Photo Gallery on my website):