Rubuta ci gaba ga wannan sakin layi - An ba Crookshank izini na biyu a cikin Royal Engineers a ranar 23 ga Yuli, 1887, an ba shi mukamin Laftanar a ranar 23 ga Yuli, 1890, kuma ya zama kyaftin a ranar 1 ga Afrilu, 1898. Ya yi aiki a Yaƙin Boer na biyu, kuma ya ji rauni kaɗan a yaƙin Paardeberg
(Fabrairu 1900). Daga nan aka sanya shi zuwa sashin Sojoji na 7 na Sojojin Afirka ta Kudu. A shekara ta 1932 an sanya shi a matsayin mai tsaron gidan Sarki.