another it is for the Army to carry out this duty. Apart from this aspect of the problem, active air defence appears to me to fall into three broad categories: (a) coast and port defence; (b) fixed and mobile ground defence; (c) active what I might term "air" defence consisting of balloon barrages and the like. Except that I think it is necessary for some definite allocation of responsibility as between our three Services (and S.I.S. is also indirectly interested), I have an open mind on the matter.