“..........Yet I doubt if many of the people know that for more than two years Germany has been turning out a million rounds of artillery ammunition a week......”
It is hard to imagine it is just big stuff. If true it would give a good jump start to Barbarossa in a couple years.
It could mean anything 20mm ir higher; it would certainly include anything 75mm or up. The Germans had a lot of light cannon shooting 37mm - anti-aircraft and anti-tank, and the Panzer III also started the war with a 37mm gun. So I think by any definition, it would include anything 37mm or above, but the article may include 20mm rounds.