Promoted to major general, from 1952 to 1955 Gentry served as Chief of the General Staff of the New Zealand Military Forces. He represented New Zealand in ANZUS and was involved in planning for the defence of Southeast Asia. In the 1954 Queen's Birthday Honours, he was made a Companion of the Order of the Bath and the following year retired from the military. In a break with convention he was not rewarded with a knighthood for his services. This may have been due to some ill-feeling within the Government regarding his work developing proposed plans for New Zealand's Middle East deployment. He was appointed knighted three years later by the newly elected Labour Government in the 1958 Queen's Birthday Honours.
