 Kọ itẹsiwaju fun paragirafi yii - Hart ṣiṣẹ ni Ogun Boer Keji lati opin ọdun 1899, akọkọ ni aṣẹ ti Northern Company of Mounted Infantry, ti o wa lakoko gbogbo awọn iṣẹ nipa Naawpoort ati Colesberg pẹlu Ẹka Ẹṣin ti Faranse fun eyiti a mẹnuba rẹ ni awọn ifiranṣẹ. O ṣe olori fun ile-iṣẹ naa ni iderun ti Kimberley 15 Kínní 1900 ati ni ilosiwaju lori Bloemfontein, pẹlu ogun Paardeberg lakoko eyiti o farapa, awọn adehun ni Driefontein, Poplar Grove, ati Klip Drift, ati ni iṣẹ ti o tẹle ti Bloemfontein ati awọn iṣẹ ila-oorun ti ilu yẹn nipa Thabanchu. Ní ìgbà ẹẹrùn ọdún 1900 ó ṣiṣẹ pẹlú Hamiltons Force ní àṣẹ fún Northern Company of Mounted Infantry àti lẹyìn náà gẹgẹ bí Staff Officer of Legges Corps of Mounted Infantry lásìkò ìlọsíwájú sí Pretoria àti gbígba Johannesburg àti Pretoria. Ó kópa nínú Ogun Diamond Hill : June 1900, ati gẹgẹbi oṣiṣẹ oṣiṣẹ ti Mounted Infantry ni igbimọ si Bethlehem ati Vredefort, lẹhin eyi ti o ṣiṣẹ bi olori brigade ti ọmọ-ogun Irish pẹlu ọwọn Oluwa Kitchener ni ibere ti Boer gbogbogbo Christiaan de Wet. 