As ever Mike aka skipman has highlighted an excellent on line source:

" The Infantry Cannot do With a Gun Less "

The place of the Artillery in the BEF 1914-1918

Mike

Source: The Infantry cannot Do With a Gun Less

A favourite of mine !!!

An interesting thesis on the development and use of Artillery in WW1

The appendices contain training notes, directives and letters which provide a contemporary documentation of evolving tactics, technical developments and lessons learned. Some nice maps show the planning of the barrages for some of the major battles, which for me shows how the Gunners were operating. The development can be tracked through the Chronological Index