In 1932 Dreyer was promoted to full admiral and in 1933 given command of the China Station where he served until 1936. He retired in 1939 only to volunteer as a Convoy Commodore in the Royal Naval Reserve upon the outbreak of the Second World War. He was on the staff of the General Officer Commanding-in-Chief, Home Forces in 1940 as an advisor on anti-invasion measure, before becoming Inspector of Merchant Navy Gunnery (1941–1942). He then was appointed as Chief of Naval Air Services (1942), before his final brief appointment as Deputy Chief of Naval Air Equipment in 1943. He then returned to the retired list for the second time. His memoirs were published as "The Sea Heritage: a Study in Maritime Warfare".