Rubuta ci gaba ga wannan sakin layi - A farkon yakin duniya na biyu Holbrook ya kasance mai koyarwa a cikin bindigogi, Sojojin Gida. Ya kasance kwamandan jami'in Rundunar Sojoji ta 73 na Tankar Tankar a lokacin yakin Arewacin Afirka tsakanin 1942 da 1943. Ya umurci rundunar soji ta 6 na Royal Artillery a lokacin mamayewar Allied na Sicily
kuma daga baya a cikin Italiya. An daukaka shi zuwa aikin brigadier a ranar 5 ga Afrilu 1943 kuma zuwa brigadier na wucin gadi a ranar 5 ga Oktoba 1943. An ambace shi a cikin sakonni a karo na biyu a ranar 24 ga Agusta, 1944, kuma a watan Disamba na 1944 an ba shi matsayin Kwamandan Dokar Daular Burtaniya. A ƙarshen yaƙin ya kasance kwamandan kwamandan Royal Artillery III Corps. Tsakanin Afrilu 1949 da Disamba 1951 Holbrook ya yi aiki a matsayin mai taimakawa ga George VI, bayan haka ya yi ritaya.