I need primary sources for artillery from ww1. I have looked everywhere such as the database of the World War I Document Archive, Proquest and archive.org but with no luck. So I am asking here as a last resort to get some help with my research.

I did find something which was this american journal from 1918.

However, I cannot find anything from the British or the German which is what I need. The source materials I need are where artillery/mortars are the main topic, because during my search i also found out many diaries touch upon the topic of artillery but most mention it as a casual thing and doesn't speak about it to the extent I need.

Any type of textual documents on the topic is highly appreciated.

Thanks beforehand.