He was director of Plans, War Office between 1939 and 1941 and became the first Chief Combined Secretary British Joint Staff Mission Washington in 1942.
"[1] In the winter of 1940–41, before the U.S. had formally entered the war, Dykes was selected for an unusual, but important mission: to escort Colonel William Joseph Donovan, soon to become head of the Office of Strategic Services (forerunner to the CIA) and head of U.S. intelligence, on a fact-finding tour of the Mediterranean.
On hearing the news, Winston Churchill sent a telegram[2] to Air Chief Marshal Sir Charles Portal asking him to send his condolences to Dykes' relatives.
[3] At the time of his death, Dykes was serving as senior British secretary to the combined Chiefs of Staffs.
He posthumously received the Distinguished Service Medal and was given a memorial service at Washington Cathedral in Washington, D.C., attended by British ambassador Lord Halifax, General George Marshall, Admiral Ernest King, Admiral Sir Percy Noble and many other dignitaries.