Made an acting colonel on 16 March 1940, Wimberley was, on 20 July 1940, shortly after the Dunkirk evacuation, promoted to the acting rank of brigadier and succeeded Brigadier Miles Dempsey in command of the 13th Brigade, part of the 5th Infantry Division. The division was then stationed in Scotland under Scottish Command, reforming after having played a distinguished part in the Battle of France, but suffering alarmingly heavy casualties in the process. The division was commanded by Major-General Horatio Berney-Ficklin, succeeding the original General Officer Commanding (GOC), Major-General Harold Franklyn, on the same day as Wimberley took command of the 13th Brigade. Wimberley was to remain with the brigade for just seven weeks, however, as in mid-September he was posted to the 152nd Infantry Brigade, part of the 51st (Highland) Infantry Division, whose GOC was then Major-General Alan Cunningham, who was replaced in late October by Major-General Neil Ritchie. On 17 October 1940 Wimberley's permanent rank was promoted to colonel, with seniority backdated to 1 January 1939.