Promoted to Major on the 29th January 1942. He was appointed to Command the 11th Battalion Worcestershire Regiment in July 1942 as Acting Lieut.-Colonel. On the 1st January 1943 the 11th Battalion was disbanded to form the basis of the reconstituted 1st Battalion Worcestershire Regiment and Lieut.-Colonel Cox continued to command the 1st Battalion until September 1943 when he left to take up a staff appointment.
As Acting Brigadier he was awarded the D.S.O. on the 1st March 1945. He also received a Mention in Despatches (London Gazette 22nd March 1945). As Temporary Brigadier he received a seconded Mention in Despatches on the 4th April 1946.
As a Major (war substantive Lieut.-Colonel) he was promoted to full rank of Lieut.-Colonel on the 18th September 1946 and on the 20th April 1949 promoted to Colonel.
In 1948 when he was with B.G.S., Western Command, he was awarded the Military Cross of the Czechoslovakian Order of the White Lion, 3rd Class, 1939. (Gazette date 14th May 1948).
On the 13th June 1953 he was promoted to Brigadier and held a staff position as Deputy Director of Infantry.
On the 1st March 1954 he was appointed Chief of Staff Southern Command and granted the temporary rank of Major-General. He held this staff role until 22nd March 1955.
Appointed General Officer Commanding Mid West District and 53rd (Welsh) Infantry Division (T.A.) on the 25th March 1955.
Promoted to Major-General on the 28th March 1955.
Major-General Cox was awarded the Companion of the Order of Bath on the 2nd January 1956.
The following year, on the 5th November 1957, he was appointed Colonel of the King's Shropshire Light Infantry. He held this appointment until 5th November 1963.
Relinquished his appointment as General Officer Commanding, Mid West District and 53rd Infantry Division (T.A.) on the 6th January 1958.