Pedzisa mutsara unotevera: Crookshank akapiwa basa rechipiri muRoyal Engineers musi wa 23 July 1887, akasimudzirwa kuva lieutenant musi wa 23 July 1890, uye kuva kaputeni musi wa 1 April 1898. Akashanda muHondo yechipiri yeBoer, uye akakuvadzwa zvishoma muhondo ye
Paardeberg (February 1900). Akabva aendeswa ku7th Infantry division yeSouth Africa Field Force. Muna 1932 akapiwa basa rokuva Murindi waMambo.