4. Air attack against troops has evidently been a major employment of air forces on both sides, though comprehensive reports are lacking. In the following paragraphs the various aspects will be discussed under the headings of attacks on trenches, on M.T. Columns, on Concentrations, on roads and lines of communication. Finally the general effect of such attacks will be considered. It should be born in mind throughout that there has been little anti-aircraft-defence against these attacks and the troops attacked were, in the majority of cases, inexperienced and untrained.