I just came across this fascinating resource and thought I'd pass it on to those who aren't yet aware of it. "Field Artillery Magazine" is available online here. They have back issues all of the way back to 1911 that are fully searchable online. Many articles are illustrated with photos or diagrams.
Enjoy, and be sure to share with the forum any especially interesting items that you turn up!
Paris Cannon - A detailed technical report written by the British before the end of the war and based largely on fragments of the shells that were collected in Paris during the bombardment!
Paris Cannon - Photos found after WWII showing the WWI testing of the Paris Gun by Krupp
There are also articles on railroad artillery, siege mortars, trucks, prime movers, & etc. - Just do a search!
I've posted a link to a great piece about 28cm howitzers (on the 28cm thread), including a photo I've never seen before of the mysterious Erhardt-Rheinmetall weapon.