Saw this on another website, it's a collection of 1000ish photo taken by the poster's great-grandfather, Lt. Walter Koessler, in WWI. Lt. Koessler was an artillery officer, and also did aerial reconnaissance.
http://wwiphotos.tumblr.com/
I like this one of early rifle grenades. (it's not up on tumblr yet)
I think they're pretty neat photos. The great-grandson is doing a kickstarter to make a book of them, for $25ish you get a digital copy of all the photos. Seems decent deal.