Air Defence Research Sub-Committee General Correspondence Correspondents include Sir Maurice Hankey, Secretary, CID (10) on his figures on the strength, training and organisation of the German air force and the progress of the Committee; Sir Philip Sassoon, Under Sec. of State for Air) on the expansion of the RAF; Desmond Morton (2) on comparison of British and German air strength; Philip Cunliffe-Lister (later Lord Swinton), Sec. of State for Air (4) on German air strength and anti-aircraft defence; Harcourt Johnstone on defence against aerial bombing; Field Marshal Lord Cavan (2) on the use of underground car parks as air raid shelters.