 At the outbreak of the Second World War , Horrocks was working as an instructor at the Staff College , Camberley , where he had taught since 1938 . After helping organise a new , shorter , officer @-@ training course , in December 1939 he was promoted to substantive lieutenant colonel . The following May , he was despatched to France to command the 2nd Battalion , Middlesex Regiment , a machine @-@ gun battalion directly subordinate to the 3rd Division headquarters of Major @-@ General Bernard Montgomery . British doctrine at the time retained heavy machine guns under the direct command of a corps or division , rather than as an organic part of subordinate formations . He joined the battalion during its retreat to Dunkirk , and after only 17 days had impressed his superiors sufficiently to be given the temporary rank of brigadier , and the command of 11th Brigade . The brigade 's previous commander , Kenneth Anderson , had been promoted to General Officer Commanding ( GOC ) 3rd Division during the evacuation , when Lieutenant @-@ General Alan Brooke , commander of II Corps , was recalled to the United Kingdom and Montgomery took over the corps . On Horrocks ' return to Britain , he was given command of 9th Brigade and assigned to defend against a possible German invasion . A short stint as Brigadier General Staff of Western Command followed , before promotion to acting major @-@ general and command of 44th ( Home Counties ) Infantry Division on 25 June 1941 . In addition to his acting rank , he was promoted to substantive colonel on 28 May 1941 ( with seniority backdated to 1 July 1940 ) . 
