(v) The provision for security cyphers, instructions etc. is necessarily made centrally. It cannot be made satisfactorily unless there is a definite general policy. It must be made long in advance. (vi) The theatre commander cannot himself "evaluate the importance of both at all times and act to attain the best compromise in the light of existing circumstances." Consideration of individual cases at individual times by the theatre commander would be impracticable. Any action by a theatre commander could be only by the issue of general instructions.