4. In the absence of any practical experience of the use of smoke screens on the scale envisaged, we suggest, however, that the possibilities of such use of smoke cannot be ignored. Accordingly we recommend that the precautions against the surprise use of smoke enumerated in Paper No.C.O.S.(40)554 (J.I.C.) should be proceeded with. 5. With regard to Conclusion (b) above, this matter is under investigation by the Ministry of Home Security. The latter, in conjunction with the Meteorological Office of the Air Ministry, have submitted a short memorandum, Paper No.J.I.C.(40)171+ in which they explain that the use of smoke as a defensive measure against air attack presents an entirely different problem to the use of smoke to cover a sea-borne invasion.