Stephen
Sorry it took me forever to find this article. It is in an old publication called Aerial Age from April 1919 that has a two page article on British Gun Cameras during the war. It was apparently mounted on a standard Lewis Gun. It is fairly detailed - if you want it I'll be glad to e-mail you a photocopy of the article - just drop me a line at my e-mail address if you want it. I've included two of the photos from it.

The first is subtitled " Mark1-A Gun Camera mounted on standard Lewis Gun". The second subtitled "Mechanism of gun camera, showing Geneva movement and shutter mechanism, which automatically continues to take phots as long as trigger is depressed". hope this all helps - let me know. John G.