Relinquishing this appointment in early 1933, Willcox was then selected to attend the Imperial Defence College, and, promoted on 8 November 1934 to lieutenant colonel, was appointed as Commanding officer (CO) of the 1st Battalion, East Lancashire Regiment. Promoted to the temporary rank of colonel on 15 September 1936, he then became Assistant Adjutant General for Palestine and Transjordan during the early stages of the Arab revolt in Palestine, before reverting to lieutenant colonel on 7 December 1936 and relinquishing the appointment on the same date. On 29 June 1937 his permanent rank was advanced to colonel (with seniority backdated to 1 July 1933) and, on the same date, was made an instructor at the Staff College, Quetta in India. He returned to England and, promoted to the temporary rank of brigadier on 16 October, took command of the 15th Infantry Brigade in succession to Brigadier Archibald Beauman. Handing over the brigade to Brigadier Horatio Berney-Ficklin in July 1939, he succeeded Brigadier Reade Godwin-Austen in command of the 13th Infantry Brigade. Both brigades formed part of the 5th Infantry Division, whose General officer commanding (GOC) was the then-Major General Harold Franklyn.